User Guide

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User Manual:

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User’s Guide for
Quantum ESPRESSO (v.6.3)

Contents
1 Introduction
1.1 People . . . . . . . . . . . .
1.2 Contacts . . . . . . . . . . .
1.3 Guidelines for posting to the
1.4 Terms of use . . . . . . . . .

. . . . . . .
. . . . . . .
mailing list
. . . . . . .

2 Installation
2.1 Download . . . . . . . . . . . . . .
2.2 Prerequisites . . . . . . . . . . . . .
2.3 configure . . . . . . . . . . . . . .
2.3.1 Manual configuration . . . .
2.4 Libraries . . . . . . . . . . . . . . .
2.5 Compilation . . . . . . . . . . . . .
2.6 Running tests and examples . . . .
2.6.1 Test-suite . . . . . . . . . .
2.6.2 Examples . . . . . . . . . .
2.7 Installation tricks and problems . .
2.7.1 All architectures . . . . . .
2.7.2 Intel Xeon Phi . . . . . . .
2.7.3 Cray machines . . . . . . .
2.7.4 IBM BlueGene . . . . . . .
2.7.5 Linux PC . . . . . . . . . .
2.7.6 Linux PC clusters with MPI
2.7.7 Microsoft Windows . . . . .
2.7.8 Mac OS . . . . . . . . . . .

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3 Parallelism
22
3.1 Understanding Parallelism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2 Running on parallel machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3 Parallelization levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
1

3.4

1

3.3.1 Understanding parallel I/O . . . . . . . . . . . . . . . . . . . . . . . . . 24
Tricks and problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Introduction

This guide gives a general overview of the contents and of the installation of Quantum
ESPRESSO (opEn-Source Package for Research in Electronic Structure, Simulation, and Optimization), version 6.3.
Important notice: due to the lack of time and of manpower, this manual does not cover
many important aspects, may contain outdated information.
The Quantum ESPRESSO distribution contains the core packages PWscf (Plane-Wave
Self-Consistent Field) and CP (Car-Parrinello) for the calculation of electronic-structure properties within Density-Functional Theory (DFT), using a Plane-Wave (PW) basis set and pseudopotentials. It also includes other packages for more specialized calculations:
• PWneb: energy barriers and reaction pathways through the Nudged Elastic Band (NEB)
method.
• PHonon: vibrational properties with Density-Functional Perturbation Theory.
• PostProc: codes and utilities for data postprocessing.
• PWcond: ballistic conductance.
• XSPECTRA: K-, L1 -, L2,3 -edge X-ray absorption spectra.
• TD-DFPT: spectra from Time-Dependent Density-Functional Perturbation Theory.
• GWL: electronic excitations within the GW approximation and with the Bethe-Salpeter
Equation
• EPW: calculation of the electron-phonon coefficients and related quantities.
The following auxiliary packages are included as well:
• PWgui: a Graphical User Interface, producing input data files for PWscf and some PostProc
codes.
• atomic: atomic calculations and pseudopotential generation.
A copy of required external libraries is also included. Finally, several additional packages that
exploit data produced by Quantum ESPRESSO or patch some Quantum ESPRESSO
routines can be automatically installed using make:
• Wannier90: maximally localized Wannier functions.
• WanT: quantum transport properties with Wannier functions.
• YAMBO: electronic excitations within Many-Body Perturbation Theory, GW and BetheSalpeter equation.
• PLUMED (v.1.3 only): calculation of free-energy surface through metadynamics.
2

• GIPAW (Gauge-Independent Projector Augmented Waves): NMR chemical shifts and EPR
g-tensor.
For Quantum ESPRESSO with the self-consistent continuum solvation (SCCS) model, aka
“Environ”, see http://www.quantum-environment.org/.
Documentation on single packages can be found in the Doc/ directory of each package.
A detailed description of input data is available for most packages in files INPUT *.txt and
INPUT *.html.
The Quantum ESPRESSO codes work on many different types of Unix machines, including parallel machines using both OpenMP and MPI (Message Passing Interface). Quantum
ESPRESSO also runs on Mac OS X and MS-Windows machines (see section 2.2). A GPUenabled version is available on https://github.com/fspiga/qe-gpu.
Further documentation, beyond what is provided in this guide, can be found in:
• the Doc/ and examples/ directories of the Quantum ESPRESSO distribution;
• the web site www.quantum-espresso.org;
• the archives of the mailing list: See section 1.2, “Contacts”, for more info.
People who want to contribute to Quantum ESPRESSO should read the Developer Manual:
Doc/developer man.pdf.
This guide does not explain the basic Unix concepts (shell, execution path, directories etc.)
and utilities needed to run Quantum ESPRESSO; it does not explain either solid state
physics and its computational methods. If you want to learn the latter, you should first read a
good textbook, such as e.g. the book by Richard Martin: Electronic Structure: Basic Theory
and Practical Methods, Cambridge University Press (2004); or: Density functional theory: a
practical introduction, D. S. Sholl, J. A. Steckel (Wiley, 2009); or Electronic Structure Calculations for Solids and Molecules: Theory and Computational Methods, J. Kohanoff (Cambridge
University Press, 2006). Then you should consult the documentation of the package you want
to use for more specific references.
All trademarks mentioned in this guide belong to their respective owners.

1.1

People

The maintenance and further development of the Quantum ESPRESSO distribution is promoted by the Quantum ESPRESSO Foundation under the coordination of Paolo Giannozzi
(Univ.Udine, Italy) with the strong support of the CINECA National Supercomputing Center
in Bologna under the responsibility of Carlo Cavazzoni.
Contributors to Quantum ESPRESSO, beyond the authors of the papers mentioned in
Sect.1.4, include:
• Ye Luo (Argonne) for improved FFT threading and miscellaneous contributions and optimization;
• Pietro Bonfà (CINECA) for multiple contributions to optimization and maintenance;
• Hsin-Yu Ho and Marcos Calegari Andrade (U.Princeton) for SCAN and other meta-GGA
functionals with libxc;

3

• Fabio Affinito (CINECA) for ELPA support, for contributions to the FFT library, and
for various parallelization improvements;
• Sebastiano Caravati for direct support of GTH pseudopotentials in analytical form, Santana Saha and Stefan Goedecker (Basel U.) for improved UPF converter of newer GTH
pseudopotentials;
• Axel Kohlmeyer for libraries and utilities to call Quantum ESPRESSO from external
codes (see the COUPLE sub-directory), made the parallelization more modular and usable
by external codes;
• Èric Germaneau for TB09 meta-GGA functional, using libxc;
• Guido Roma (CEA Saclay) for vdw-df-obk8 e vdw-df-ob86 functionals;
• Yves Ferro (Univ. Provence) for SOGGA and M06L functionals;
• Ikutaro Hamada (NIMS, Japan) for OPTB86B-vdW, REV-vdW-DF2 functionals, fixes
to pw2xsf utility;
• Daniel Forrer (Padua Univ.) and Michele Pavone (Naples Univ. Federico II) for dispersions interaction in the framework of DFT-D;
• Filippo Spiga (University of Cambridge, UK) for mixed MPI-OpenMP parallelization and
for the GPU-enabled version;
• Costas Bekas and Alessandro Curioni (IBM Zurich) for the initial BlueGene porting.
Contributors to specific Quantum ESPRESSO packages are acknowledged in the documentation of each package.
An alphabetic list of further contributors who answered questions on the mailing list, found
bugs, helped in porting to new architectures, wrote some code, contributed in some way or
another at some stage, follows:
Åke Sandgren, Audrius Alkauskas, Alain Allouche, Francesco Antoniella, Uli Aschauer, Francesca Baletto, Gerardo Ballabio, Mauro Boero, Scott Brozell, Claudia
Bungaro, Paolo Cazzato, Gabriele Cipriani, Jiayu Dai, Stefano Dal Forno, Cesar Da
Silva, Alberto Debernardi, Gernot Deinzer, Alin Marin Elena, Francesco Filipponi,
Prasenjit Ghosh, Marco Govoni, Thomas Gruber, Martin Hilgeman, Yosuke Kanai,
Konstantin Kudin, Nicolas Lacorne, Hyungjun Lee, Stephane Lefranc, Sergey Lisenkov,
Kurt Maeder, Andrea Marini, Giuseppe Mattioli, Nicolas Mounet, William Parker,
Pasquale Pavone, Samuel Poncé, Mickael Profeta, Chung-Yuan Ren, Kurt Stokbro,
David Strubbe, Sylvie Stucki, Paul Tangney, Pascal Thibaudeau, Davide Tiana,
Antonio Tilocca, Jaro Tobik, Malgorzata Wierzbowska, Vittorio Zecca, Silviu Zilberman, Federico Zipoli,
and let us apologize to everybody we have forgotten.

4

1.2

Contacts

The web site for Quantum ESPRESSO is http://www.quantum-espresso.org/. Releases
and patches can be downloaded from this site or following the links contained in it. The main
entry point for developers is the GitLab web site: https://gitlab.com/QEF/q-e.
The recommended place where to ask questions about installation and usage of Quantum
ESPRESSO, and to report problems, is the mailing list users@lists.quantum-espresso.org.
Here you can obtain help from the developers and from knowledgeable users. You have to be
subscribed (see the “Contacts” section of the web site) in order to post to the users’ list. Please
read the guidelines for posting, section 1.3! NOTA BENE: only messages that appear to come
from the registered user’s e-mail address, in its exact form, will be accepted. Messages ”waiting
for moderator approval” are automatically deleted with no further processing (sorry, too much
spam). In case of trouble, carefully check that your return e-mail is the correct one (i.e. the
one you used to subscribe).
If you need to contact the developers for specific questions about coding, proposals, offers
of help, etc., you may either post an “Issue” to GitLab, or send a message to the developers’
mailing list developers@lists.quantum-espresso.org. Please do not post general questions
there: they will be ignored.

1.3

Guidelines for posting to the mailing list

Life for mailing list subscribers will be easier if everybody complies with the following guidelines:
• Before posting, please: browse or search the archives – links are available in the “Contacts”
section of the web site. Most questions are asked over and over again. Also: make an
attempt to search the available documentation, notably the FAQs and the User Guide(s).
The answer to most questions is already there.
• Reply to both the mailing list and the author or the post, using “Reply to all”.
• Sign your post with your name and affiliation.
• Choose a meaningful subject. Do not use ”reply” to start a new thread: it will confuse
the ordering of messages into threads that most mailers can do. In particular, do not use
”Reply” to a Digest!!!
• Be short: no need to send 128 copies of the same error message just because this is what
came out of your 128-processor run. No need to send the entire compilation log for a
single error appearing at the end.
• Do not post large attachments: point a linker to a place where the attachment(s) can
be downloaded from, such as e.g. DropBox, Google Docs, or one of the various web
temporary storage spaces (e.g.: ExpireBox, File.Town, Uguu.se).
• Avoid excessive or irrelevant quoting of previous messages. Your message must be immediately visible and easily readable, not hidden into a sea of quoted text.
• Remember that even experts cannot guess where a problem lies in the absence of sufficient
information. One piece of information that must always be provided is the version number
of Quantum ESPRESSO.
5

• Remember that the mailing list is a voluntary endeavor: nobody is entitled to an answer,
even less to an immediate answer.
• Finally, please note that the mailing list is not a replacement for your own work, nor is
it a replacement for your thesis director’s work.

1.4

Terms of use

Quantum ESPRESSO is free software, released under the GNU General Public License.
See http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt, or the file License in the
distribution).
We shall greatly appreciate if scientific work done using the Quantum ESPRESSO distribution will contain an acknowledgment to the following references:
P. Giannozzi, S. Baroni, N. Bonini, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli,
G. L. Chiarotti, M. Cococcioni, I. Dabo, A. Dal Corso, S. Fabris, G. Fratesi, S. de
Gironcoli, R. Gebauer, U. Gerstmann, C. Gougoussis, A. Kokalj, M. Lazzeri, L.
Martin-Samos, N. Marzari, F. Mauri, R. Mazzarello, S. Paolini, A. Pasquarello, L.
Paulatto, C. Sbraccia, S. Scandolo, G. Sclauzero, A. P. Seitsonen, A. Smogunov, P.
Umari, R. M. Wentzcovitch, J.Phys.: Condens.Matter 21, 395502 (2009)
and
P. Giannozzi, O. Andreussi, T. Brumme, O. Bunau, M. Buongiorno Nardelli, M.
Calandra, R. Car, C. Cavazzoni, D. Ceresoli, M. Cococcioni, N. Colonna, I. Carnimeo, A. Dal Corso, S. de Gironcoli, P. Delugas, R. A. DiStasio Jr, A. Ferretti, A.
Floris, G. Fratesi, G. Fugallo, R. Gebauer, U. Gerstmann, F. Giustino, T. Gorni, J
Jia, M. Kawamura, H.-Y. Ko, A. Kokalj, E. Küçükbenli, M .Lazzeri, M. Marsili, N.
Marzari, F. Mauri, N. L. Nguyen, H.-V. Nguyen, A. Otero-de-la-Roza, L. Paulatto,
S. Poncé, D. Rocca, R. Sabatini, B. Santra, M. Schlipf, A. P. Seitsonen, A. Smogunov, I. Timrov, T. Thonhauser, P. Umari, N. Vast, X. Wu, S. Baroni J.Phys.:
Condens.Matter 29, 465901 (2017)
Note the form Quantum ESPRESSO for textual citations of the code. Please also see
package-specific documentation for further recommended citations. Pseudopotentials should
be cited as (for instance)
[ ] We used the pseudopotentials C.pbe-rrjkus.UPF and O.pbe-vbc.UPF from
http://www.quantum-espresso.org.

2
2.1

Installation
Download

Presently, Quantum ESPRESSO is distributed in source form. Packages for the Debian
Linux distribution are however made available by debichem developers. Stable releases of the
Quantum ESPRESSO source package (current version is 6.3) can be downloaded from the
links listed in the “Download” section of www.quantum-espresso.org.
Uncompress and unpack the base distribution using the command:
6

tar zxvf qe-X.Y.Z.tar.gz
(a hyphen before ”zxvf” is optional) where X.Y.Z stands for the version number. If your version
of tar doesn’t recognize the ”z” flag:
gunzip -c qe-X.Y.Z.tar.gz | tar xvf A directory qe-X.Y.Z/ will be created.
Additional packages that are not included in the base distribution will be downloaded on
demand at compile time, using make (see Sec.2.5). Note however that this will work only if
the computer you are installing on is directly connected to the internet and has either wget or
curl installed and working. If you run into trouble, manually download each required package
into subdirectory archive/, not unpacking or uncompressing it: command make will take care
of this during installation.
The Quantum ESPRESSO distribution contains several directories. Some of them are
common to all packages:
Modules/
Fortran modules and utilities used by all programs
include/
files *.h included by fortran and C source files
clib/
libraries and utilities written in C
FFTXlib/
FFT libraries
LAXlib/
Linear Algebra (parallel) libraries
KS Solvers/ Iterative diagonalization routines
UtilXlib/
Miscellaneous timing, error handling, MPI utilites
install/
installation scripts and utilities
pseudo/
pseudopotential files used by examples
upftools/
converters to unified pseudopotential format (UPF)
Doc/
general documentation
archive/
external libraries in .tar.gz form
test-suite/ automated tests
while others are specific to a single package:
PW/
PWscf package
EPW/
EPW package
NEB/
PWneb package
PP/
PostProc package
PHonon/ PHonon package
PWCOND/ PWcond package
CPV/
CP package
atomic/ atomic package
GUI/
PWGui package
Finally, directory COUPLE/ contains code and documentation that is useful to call Quantum
ESPRESSO programs from external codes; directory LR Modules/ contains source files for
modules that are common to all linear-response codes.

2.2

Prerequisites

To install Quantum ESPRESSO from source, you need first of all a minimal Unix environment, that is: a command shell (e.g., bash, sh) and utilities make, awk, sed. For MS-Windows,
see Sec.2.7.7.
7

Note that the scripts contained in the distribution assume that the local language is set to
the standard, i.e. ”C”; other settings may break them. Use export LC ALL=C (sh/bash) or
setenv LC ALL C (csh/tcsh) to prevent any problem when running scripts (including installation scripts).
Second, you need C and Fortran compilers, compliant with C89 and F2003 standards. For
parallel execution, you will also need MPI libraries and a parallel (i.e. MPI-aware) compiler.
For massively parallel machines, or for simple multicore parallelization, an OpenMP-aware
compiler and libraries are also required.
As a rule, Quantum ESPRESSO tries to keep compatibility with older compilers, avoiding
nonstandard extensions and newer features that are not widespread or stabilized. No warranty,
however, if your compiler is older than ∼ 5 years or so. The same applies to mathematical and
MPI libraries.
Big machines with specialized hardware (e.g. IBM SP, CRAY, etc) typically have a Fortran compiler with MPI and OpenMP libraries bundled with the software. Workstations or
“commodity” machines, using PC hardware, may or may not have the needed software. If not,
you need either to buy a commercial product (e.g Intel, NAG, PGI) or to use an open-source
compiler like gfortran from the gcc distribution. Some commercial compilers (e.g. PGI) may
be available free of charge under some conditions (e.g. academic or personal usage).

2.3

configure

To install the Quantum ESPRESSO source package, run the configure script. This is
actually a wrapper to the true configure, located in the install/ subdirectory (configure
-h for help). configure will (try to) detect compilers and libraries available on your machine,
and set up things accordingly. Presently it is expected to work on most Linux 32- and 64-bit
PCs (all Intel and AMD CPUs) and PC clusters, IBM BlueGene machines, NEC SX, Cray
XT machines, Mac OS X, MS-Windows PCs. Detailed but sometimes outdated installation
instructions for specific HPC machines may be found in files install/README.sys, where sys
is the machine name.
Instructions for the impatient:
cd qe-X.Y.Z/
./configure
make all
This will (try to) produce parallel (MPI) executable if a proper parallel environment is detected,
serial executables otherwise. For OpenMP executables, specify ./configure --enable-openmp.
Symlinks to executable programs will be placed in the bin/ subdirectory. Note that both C
and Fortran compilers must be in your execution path, as specified in the PATH environment
variable. Additional instructions for special machines:
./configure ARCH=crayxt4
for CRAY XT machines
./configure ARCH=necsx
for NEC SX machines
./configure ARCH=ppc64-mn PowerPC Linux + xlf (Marenostrum)
./configure ARCH=ppc64-bg IBM BG/P (BlueGene)
configure generates the following files:

8

compilation rules and flags (used by Makefile)
a report of the configuration run (not needed for compilation)
detailed log of the configuration run (useful for debugging)
a few definitions used by C files
info on compilation flags (not used: in Modules/environment.f90
uncomment #define __HAVE_CONFIG_INFO to enable its usage)
NOTA BENE: configure no longer updates dependencies. If you modify the sources, run
./install/makedeps.sh or type make depend to update files make.depend in the various
subdirectories.
NOTA BENE 2: make.inc used to be called make.sys until v.6.0. The change of name is due
to frequent problems with mailers assuming that whatever ends in .sys is a suspect virus.
You should always be able to compile the Quantum ESPRESSO suite of programs without
having to edit any of the generated files. However you may have to tune configure by specifying
appropriate environment variables and/or command-line options. Usually the tricky part is to
get external libraries recognized and used: see Sec.2.4 for details and hints.
Environment variables may be set in any of these ways:
make.inc
install/configure.msg
install/config.log
include/c defs.h
include/configure.h

export VARIABLE=value; ./configure
setenv VARIABLE value; ./configure
env VARIABLE=value ./configure
./configure VARIABLE=value

#
#
#
#

sh, bash, ksh
csh, tcsh
any shell
any shell

Some environment variables that are relevant to configure are:
ARCH
label identifying the machine type (see below)
F90, F77, CC
names of Fortran, Fortran-77, and C compilers
MPIF90
name of parallel Fortran 90 compiler (using MPI)
CPP
source file preprocessor (defaults to $CC -E)
LD
linker (defaults to $MPIF90)
(C,F,F90,CPP,LD)FLAGS compilation/preprocessor/loader flags
LIBDIRS
extra directories where to search for libraries
(note that “F90” is an historical name: we actually use F2003) For example, the following
command line:
./configure MPIF90=mpif90 FFLAGS="-O2 -assume byterecl" \
CC=gcc CFLAGS=-O3 LDFLAGS=-static
instructs configure to use mpif90 as Fortran compiler with flags -O2 -assume byterecl,
gcc as C compiler with flags -O3, and to link with flag -static. Note that the value of
FFLAGS must be quoted, because it contains spaces. NOTA BENE: do not pass compiler names
with the leading path included. F90=f90xyz is ok, F90=/path/to/f90xyz is not. Do not use
environment variables with configure unless they are needed! try configure with no options
as a first step.
If your machine type is unknown to configure, you may use the ARCH variable to suggest
an architecture among supported ones. Some large parallel machines using a front-end (e.g.
Cray XT) will actually need it, or else configure will correctly recognize the front-end but not
the specialized compilation environment of those machines. In some cases, cross-compilation
requires to specify the target machine with the --host option. This feature has not been
extensively tested, but we had at least one successful report (compilation for NEC SX6 on a
PC). Currently supported architectures are:
9

ia32
Intel 32-bit machines (x86) running Linux
ia64
Intel 64-bit (Itanium) running Linux
Intel and AMD 64-bit running Linux - see note below
x86 64
crayxt4
Cray XT4/XT5/XE machines
mac686
Apple Intel machines running Mac OS X
cygwin
MS-Windows PCs with Cygwin
mingw32
Cross-compilation for MS-Windows, using mingw, 32 bits
mingw64
As above, 64 bits
necsx
NEC SX-6 and SX-8 machines
ppc64
Linux PowerPC machines, 64 bits
ppc64-mn as above, with IBM xlf compiler
ppc64-bg IBM BlueGene
arm
ARM machines (with gfortran)
Note: x86 64 replaces amd64 since v.4.1. Cray Unicos machines, SGI machines with MIPS
architecture, HP-Compaq Alphas are no longer supported since v.4.2; PowerPC Macs are no
longer supported since v.5.0. IBM machines with AIX are no longer supported since v.6.0.
Finally, configure recognizes the following command-line options:
--enable-parallel compile for parallel (MPI) execution if possible (default: yes)
--enable-openmp
compile for OpenMP execution if possible (default: no)
--enable-shared
use shared libraries if available (default: yes;
”no” is implemented, untested, in only a few cases)
--enable-debug
compile with debug flags (only for selected cases; default: no)
--enable-signals
enable signal trapping (default: disabled)
and the following optional packages:
--with-internal-blas
compile with internal BLAS (default: no)
--with-internal-lapack compile with internal LAPACK (default: no)
--with-scalapack
(yes|no|intel) Use scalapack if available.
Set to intel to use Intel MPI and blacs (default: use OpenMPI)
--with-elpa-include
Specify full path of ELPA include and modules headers (default: no)
--with-elpa-lib
Specify full path of the ELPA library (default: no)
--with-elpa-version
Specify ELPA version, only year (2015 or 2016, default: 2016)
--with-hdf5
(no | ) Write portable binary files using HDF5.
A valid  for HDF5 library must be specified (default: no)
The following options are available for the CUDA Fortran accelerated version (currently in
a separate package, not yet included in the main distribution):

10

enables compilation of the CUDA Fortran
accelerated subroutines.
value should point the path where the CUDA toolkit
is installed, e.g. /opt/cuda (default: no)
--with-cuda-cc=value
sets the compute capabilities for the compilation
of the accelerated subroutines.
value must be consistent with the hardware and the
NVidia driver installed on the workstation or on the
compute nodes of the HPC facility (default: 35)
--with-cuda-runtime=value sets the version of the CUDA toolkit used
for the compilation of the accelerated code.
value must be consistent with the
CUDA Toolkit installed on the workstation
or available on the compute nodes of the HPC facility.
PGI compilers currently accept 7.5, 8.0 or 9.0 (default: 8.0)

--with-cuda=value

Please note that in order to compile the CUDA Fortran code you need ... the CUDA Fortran
code (it is not yet available in the main distribution)! you also need a recent version of the
PGI Fortran compilers (at least 17.4). OpenMP must be enabled, and you may want to use a
CUDA-aware MPI distribution to optimize the data transfer between the processes.
If you want to modify configure (advanced users only!), see the Developer Manual.
2.3.1

Manual configuration

If configure stops before the end, and you don’t find a way to fix it, you have to write
a working make.inc file (optionally, include/c defs.h). The template used by configure
is install/make.inc.in and contains explanations of the meaning of the various variables.
Note that you may need to select appropriate preprocessing flags in conjunction with the
desired or available libraries (e.g. you need to add -D FFTW to DFLAGS if you want to link
internal FFTW). For a correct choice of preprocessing flags, refer to the documentation in
include/defs.h.README.
NOTA BENE: If you change any settings (e.g. preprocessing, compilation flags) after a
previous (successful or failed) compilation, you must run make clean before recompiling, unless
you know exactly which routines are affected by the changed settings and how to force their
recompilation. configure will clean object and executables, unless you use option --save.

2.4

Libraries

Quantum ESPRESSO makes use of the following external libraries:
• BLAS (http://www.netlib.org/blas/) and
• LAPACK (http://www.netlib.org/lapack/) for linear algebra
• FFTW (http://www.fftw.org/) for Fast Fourier Transforms
A copy of the needed routines is provided with the distribution. However, when available,
optimized vendor-specific libraries should be used: this often yields huge performance gains.

11

BLAS and LAPACK Quantum ESPRESSO can use any architecture-optimized BLAS
and LAPACK replacements, like those contained e.g. in the following libraries:
MKL for Intel CPUs
ACML for AMD CPUs
ESSL for IBM machines
If none of these is available, we suggest that you use the optimized ATLAS library: see
http://math-atlas.sourceforge.net/. Note that ATLAS is not a complete replacement for
LAPACK: it contains all of the BLAS, plus the LU code, plus the full storage Cholesky code.
Follow the instructions in the ATLAS distributions to produce a full LAPACK replacement.
Sergei Lisenkov reported success and good performances with optimized BLAS by Kazushige
Goto. The library is now available under an open-source license: see the GotoBLAS2 page at
http://www.tacc.utexas.edu/tacc-software/gotoblas2/.
FFT Quantum ESPRESSO has an internal copy of an old FFTW library. It also supports
the newer FFTW3 library and some vendor-specific FFT libraries. configure will first search
for vendor-specific FFT libraries; if none is found, it will search for an external FFTW v.3
library; if none is found, it will fall back to the internal copy of FFTW. configure will add
the appropriate preprocessing options:
• -D LINUX ESSL for ESSL on IBM Linux machines,
• -DASL for NEC ASL library on NEC machines,
• -D ARM LIB for ARM Performance library,
• -D DFTI for DFTI (Intel MKL library),
• -D FFTW3 for FFTW3 (external),
• -D FFTW for FFTW (internal library),
to DFLAGS in the make.inc file. If you edit make.inc manually, please note that one and only
one among the mentioned preprocessing option must be set.
If you have MKL libraries, you may either use the provided FFTW3 interface (v.10 and
later), or directly link FFTW3 from MKL (v.12 and later) or use DFTI (recommended).
MPI libraries MPI libraries are usually needed for parallel execution, unless you are happy
with OpenMP-only multicore parallelization. In well-configured machines, configure should
find the appropriate parallel compiler for you, and this should find the appropriate libraries.
Since often this doesn’t happen, especially on PC clusters, see Sec.2.7.6.
Note: since v.6.1, MPI libraries implementing v.3 of the standard (notably, non-blocking
broadcast and gather operations) are required.
Libraries for accelerators The accelerated version of the code uses standard CUDA libraries
such as cublas, cufft, cusolver and the eigensolver library explicitly developed for Quantum ESPRESSO by NVidia and distributed at https://github.com/NVIDIA/Eigensolver gpu.
12

HDF5 The HDF5 library (https://www.hdfgroup.org/downloads/hdf5/) can be used to
perform binary I/O using the HDF5 format.
The user may need to install this library, compiling it with options --enable-fortran,
--enable-fortran-2003, and --enable-parallel (see below). These options must be passed
to the configure script of the library, not of Quantum ESPRESSO.
The path to the root directory of the library (the one containing bin/, include/ and
lib/ directories) has to be passed to the configure script of Quantum ESPRESSO via the
--with-hdf5=... option.
It is possible to use a library with disabled parallelism, but one has to add manually the
flag -D HDF5 SERIAL to the MANUAL DFLAGS in the make.inc file.
The HDF5 packages provided by many LINUX distributions may also work, but the configure script fails if includes and libraries are not placed under the same root directory. In this
case the user should manually set the correct paths in the make.inc file.
Other libraries Quantum ESPRESSO can use the MASS vector math library from IBM,
if available (only on machines with XLF compiler: likely obsolete).
If optimized libraries are not found The configure script attempts to find optimized
libraries, but may fail if they have been installed in non-standard places. You should examine the final value of BLAS LIBS, LAPACK LIBS, FFT LIBS, MPI LIBS (if needed), MASS LIBS
(IBM only), either in the output of configure or in the generated make.inc, to check whether
it found all the libraries that you intend to use.
If some library was not found, you can specify a list of directories to search in the environment variable LIBDIRS, and rerun configure; directories in the list must be separated by
spaces. For example:
./configure LIBDIRS="/opt/intel/mkl70/lib/32 /usr/lib/math"
If this still fails, you may set some or all of the * LIBS variables manually and retry. For
example:
./configure BLAS_LIBS="-L/usr/lib/math -lf77blas -latlas_sse"
Beware that in this case, configure will blindly accept the specified value, and won’t do any
extra search.

2.5

Compilation

There are a few adjustable parameters in Modules/parameters.f90. The present values will
work for most cases. All other variables are dynamically allocated: you should never need to
recompile your code.
At your choice, you may compile the complete Quantum ESPRESSO suite of programs
(with make all), or only some specific programs. make with no arguments yields a list of valid
compilation targets:
• make pw compiles the self-consistent-field package PWscf
• make cp compiles the Car-Parrinello package CP

13

• make neb compiles the PWneb package. All executables are linked in main bin directory
• make ph compiles the PHonon package. All executables are linked in main bin directory
• make pp compiles the postprocessing package PostProc
• make pwcond compiles the ballistic conductance package PWcond. All executables are
linked in main bin directory
• make pwall produces all of the above.
• make ld1 compiles the pseudopotential generator package atomic. All executables are
linked in main bin directory
• make xspectra compiles the package XSpectra. All executables are linked in main bin
directory
• make upf produces utilities for pseudopotential conversion in directory upftools/
• make all produces all of the above
• make epw compiles package EPW
• make plumed unpacks PLUMED, patches several routines in PW/, CPV/ and clib/, recompiles PWscf and CP with PLUMED support
• make w90 downloads wannier90, unpacks it, copies an appropriate make.inc file, produces all executables in W90/wannier90.x and in bin/
• make want downloads WanT, unpacks it, runs its configure, produces all executables for
WanT in WANT/bin.
• make yambo downloads yambo, unpacks it, runs its configure, produces all yambo executables in YAMBO/bin
• make gipaw downloads GIPAW, unpacks it, runs its configure, produces all GIPAW executables in GIPAW/bin and in main bin directory.
For the setup of the GUI, refer to the PWgui-X.Y.Z /INSTALL file, where X.Y.Z stands for the
version number of the GUI (should be the same as the general version number). If you are
using sources from the git repository, see the GUI/README file instead.
If make refuses for some reason to download additional packages, manually download them
into subdirectory archive/, not unpacking or uncompressing them, and try make again. Also
see Sec.(2.1).

2.6

Running tests and examples

As a final check that compilation was successful, you may want to run some or all of the tests
and examples. Notice that most tests and examples are devised to be run serially or on a small
number of processors; do not use tests and examples to benchmark parallelism, do not try to
run on too many processors.

14

2.6.1

Test-suite

Automated tests give a ”pass/fail” answer. All tests run quickly (less than a minute at most),
but they are not meant to be realistic, just to test a specific case. Many features are tested but
only for the following codes: pw.x, cp.x, ph.x, epw.x. Instructions for the impatient:
cd test-suite
make run-tests
Instructions for all others: go to the test-suite/ directory, read the README file, or at least,
type make. You may need to edit the run-XX.sh shells, defining variables PARA PREFIX and
PARA POSTFIX (see below for their meaning).
2.6.2

Examples

There are many examples and reference data for almost every piece of Quantum ESPRESSO,
but you have to manually inspect the results.
In order to use examples, you should edit file environment variables, setting the following
variables as needed.
BIN DIR: directory where executables reside
PSEUDO DIR: directory where pseudopotential files reside
TMP DIR: directory to be used as temporary storage area
The default values of BIN DIR and PSEUDO DIR should be fine, unless you have installed
things in nonstandard places. TMP DIR must be a directory where you have read and write
access to, with enough available space to host the temporary files produced by the example
runs, and possibly offering high I/O performance (i.e., don’t use an NFS-mounted directory).
NOTA BENE: do not use a directory containing other data: the examples will clean it!
If you have compiled the parallel version of Quantum ESPRESSO (this is the default
if parallel libraries are detected), you will usually have to specify a launcher program (such
as mpirun or mpiexec) and the number of processors: see Sec.3 for details. In order to do
that, edit again the environment variables file and set the PARA PREFIX and PARA POSTFIX
variables as needed. Parallel executables will be run by a command like this:
$PARA_PREFIX pw.x $PARA_POSTFIX -i file.in > file.out
For example, if the command line is like this (as for an IBM SP):
poe pw.x -procs 4 -i file.in > file.out
you should set PARA PREFIX="poe", PARA POSTFIX="-procs 4". Furthermore, if your machine
does not support interactive use, you must run the commands specified above through the batch
queuing system installed on that machine. Ask your system administrator for instructions. For
execution using OpenMP on N threads, use PARA PREFIX="env OMP NUM THREADS=N ... ".
To run an example, go to the corresponding directory (e.g. PW/examples/example01) and
execute:
./run_example

15

This will create a subdirectory results/, containing the input and output files generated by
the calculation. Some examples take only a few seconds to run, while others may require up to
several minutes.
In each example’s directory, the reference/ subdirectory contains verified output files,
that you can check your results against. They were generated on a Linux PC using the Intel
compiler. On different architectures the precise numbers could be slightly different, in particular
if different FFT dimensions are automatically selected. For this reason, a plain diff of your
results against the reference data doesn’t work, or at least, it requires human inspection of the
results.
The example scripts stop if an error is detected. You should look inside the last written
output file to understand why.

2.7
2.7.1

Installation tricks and problems
All architectures

• Working Fortran and C compilers, compliant with F2003 and C89 standards respectively,
are needed in order to compile Quantum ESPRESSO. Most recent Fortran compilers
will do the job.
C and Fortran compilers must be in your PATH. If configure says that you have no
working compiler, well, you have no working compiler, at least not in your PATH, and
not among those recognized by configure.
• If you get Compiler Internal Error or similar messages: your compiler version is buggy.
Try to lower the optimization level, or to remove optimization just for the routine that
has problems. If it doesn’t work, or if you experience weird problems at run time, try
to install patches for your version of the compiler (most vendors release at least a few
patches for free), or to upgrade to a more recent compiler version.
• If you get error messages at the loading phase that look like file XYZ.o: unknown / not
recognized/ invalid / wrong file type / file format / module version, one of the following
things have happened:
1. you have leftover object files from a compilation with another compiler: run make
clean and recompile.
2. make did not stop at the first compilation error (it may happen in some software
configurations). Remove the file *.o that triggers the error message, recompile, look
for a compilation error.
If many symbols are missing in the loading phase: you did not specify the location of all
needed libraries (LAPACK, BLAS, FFTW, machine-specific optimized libraries), in the
needed order. Note that Quantum ESPRESSO is self-contained (with the exception
of MPI libraries for parallel compilation): if system libraries are missing, the problem is
in your compiler/library combination or in their usage, not in Quantum ESPRESSO.
• If you get mysterious Segmentation fault and the like errors in the provided tests and
examples: your compiler, or your mathematical libraries, or MPI libraries, or a combination thereof, is very likely buggy, or there is some form of incompatibility (see below).
16

Although one can never rule out the presence of subtle bugs in Quantum ESPRESSO
that are not revealed during the testing phase, it is very unlikely that this happens on
the provided tests and examples.
2.7.2

Intel Xeon Phi

For Intel Xeon CPUs with Phi coprocessor, there are three ways of compiling:
• offload mode, executed on main CPU and offloaded onto coprocessor ”automagically”;
• native mode, executed completely on coprocessor;
• symmetric mode, requiring creation of both binaries.
”You can take advantage of the offload mode using the libxphi library. This library offloads the
BLAS/MKL functions on the Xeon Phi platform hiding the latency times due to the communication. You just need to compile this library and then to link it dynamically. The library works
with any version of QE. Libxphi is available from https://github.com/cdahnken/libxphi.
Some documentation is available therein.
Instead, if you want to compile a native version of QE, you just need to add the -mmic flag
and cross compile. If you want to use the symmetric mode, you need to compile twice: with
and without the -mmic flag”. ”[...] everything, i.e. code+libraries, must be cross-compiled
with the -mmic flag. In my opinion, it’s pretty unlikely that native mode can outperform the
execution on the standard Xeon cpu. I strongly suggest to use the Xeon Phi in offload mode,
for now” (info by Fabio Affinito, March 2015).
2.7.3

Cray machines

(This section is likely obsolete)
For Cray XE machines:
$ module swap PrgEnv-cray PrgEnv-pgi
$ ./configure --enable-openmp --enable-parallel --with-scalapack
$ vim make.inc
then manually add -D IOTK WORKAROUND1 at the end of DFLAGS line.
”Now, despite what people can imagine, every CRAY machine deployed can have different
environment. For example on the machine I usually use for tests [...] I do have to unload some
modules to make QE running properly. On another CRAY [...] there is also Intel compiler as
option and the system is slightly different compared to the other. So my recipe should work,
99% of the cases.” (info by Filippo Spiga)
For Cray XT machines, use ./configure ARCH=crayxt4 or else configure will not recognize the Cray-specific software environment.
Older Cray machines: T3D, T3E, X1, are no longer supported.
2.7.4

IBM BlueGene

The current configure was working on the machines at CINECA and at Jülich. For other
machines, you may need something like

17

./configure ARCH=ppc64-bg BLAS_LIBS=... LAPACK_LIBS=... \
SCALAPACK_DIR=... BLACS_DIR=..."
where the various * LIBS and * DIR ”suggest” where the various libraries are located.
2.7.5

Linux PC

Both AMD and Intel CPUs, 32-bit and 64-bit, are supported and work, either in 32-bit emulation and in 64-bit mode. 64-bit executables can address a much larger memory space than
32-bit executable, but there is no gain in speed. Beware: the default integer type for 64-bit
machine is typically 32-bit long. You should be able to use 64-bit integers as well, but it is not
guaranteed to work and will not give any advantage anyway.
Currently, configure supports Intel (ifort), NAG (nagfor), PGI (pgf90) and gfortran compilers. Pathscale, Sun Studio, AMD Open64, are no longer supported after v.6.2: g95, since
v.6.1.
Both Intel MKL and AMD acml mathematical libraries are supported, the former much
better than the latter.
It is usually convenient to create semi-statically linked executables (with only libc, libm,
libpthread dynamically linked). If you want to produce a binary that runs on different machines,
compile it on the oldest machine you have (i.e. the one with the oldest version of the operating
system).

Linux PCs with gfortran You need at least gfortran v.4.4 or later to properly compile
Quantum ESPRESSO.
”There is a known incompatibility problem between the calling convention for Fortran functions that return complex values: there is the convention used by g77/f2c, where in practice
the compiler converts such functions to subroutines with a further parameter for the return
value; gfortran instead produces a normal function returning a complex value. If your system
libraries were compiled using g77 (which may happen for system-provided libraries in not-toorecent Linux distributions), and you instead use gfortran to compile Quantum ESPRESSO,
your code may crash or produce random results. This typically happens during calls to zdotc,
which is one the most commonly used complex-returning functions of BLAS+LAPACK.
For further details see for instance this link:
http://www.macresearch.org/lapackblas-fortran-106#comment-17071
or read the man page of gfortran under the flag -ff2c.
If your code crashes during a call to zdotc, try to recompile Quantum ESPRESSO using
the internal BLAS and LAPACK routines (using the --with-internal-blas and --with-internal-lap
parameters of the configure script) to see if the problem disappears; or, add the -ff2c flag”
(info by Giovanni Pizzi, Jan. 2013).
Note that a similar problem with complex functions exists with MKL libraries as well: if
you compile with gfortran, link -lmkl gf lp64, not -lmkl intel lp64, and the like for other
architectures. Since v.5.1, you may use the following workaround: add preprocessing option
-Dzdotc=zdotc wrapper to DFLAGS.
Linux PCs with Intel compiler (ifort) The Intel compiler ifort http://software.intel.com/
produces fast executables, at least on Intel CPUs, but not all versions work as expected (see
below). In case of trouble, update your version with the most recent patches. Since each major
18

release of ifort differs a lot from the previous one, compiled objects from different releases may
be incompatible and should not be mixed.
The Intel compiler is no longer free for personal usage, but it is still for students and opensource contributors (https://software.intel.com/en-us/qualify-for-free-software).
If configure doesn’t find the compiler, or if you get Error loading shared libraries at run
time, you may have forgotten to execute the script that sets up the correct PATH and library
path. Unless your system manager has done this for you, you should execute the appropriate
script – located in the directory containing the compiler executable – in your initialization files.
Consult the documentation provided by Intel.
The warning: feupdateenv is not implemented and will always fail, can be safely ignored.
Warnings on “bad preprocessing option” when compiling iotk and complains about “recommended formats” may also be ignored.
The following compiler releases are known to give segmentation faults in at least some cases
of compilation of Quantum ESPRESSO v.6.0:
12.0.0.084
12.0.1.107
12.0.2.137
12.0.4.191
12.0.5.220
16.0.1.150

Build
Build
Build
Build
Build
Build

20101006
20101116
20110112
20110427
20110719
20151021

(Filippo Spiga, Aug. 2016)
ifort v.12: release 12.0.0 miscompiles iotk, leading to mysterious errors when reading data
files. Workaround: increase the parameter BLOCKSIZE to e.g. 131072*1024 when opening
files in iotk/src/iotk files.f90 (info by Lorenzo Paulatto, Nov. 2010).
ifort v.11: Segmentation faults were reported for the combination ifort 11.0.081, MKL
10.1.1.019, OpenMP 1.3.3. The problem disappeared with ifort 11.1.056 and MKL 10.2.2.025
(Carlo Nervi, Oct. 2009).
Linux PCs with MKL libraries On Intel CPUs it is very convenient to use Intel MKL
libraries (freely available at https://software.intel.com/en-us/performance-libraries).
MKL libraries can be used also with non-Intel compilers. They work also for AMD CPU,
selecting the appropriate machine-optimized libraries, but with reduced performances.
configure should recognize properly installed MKL libraries. By default the non-threaded
version of MKL is linked, unless option configure --with-openmp is specified. In case of
trouble, refer to the following web page to find the correct way to link MKL:
http://software.intel.com/en-us/articles/intel-mkl-link-line-advisor/.
For parallel (MPI) execution on multiprocessor (SMP) machines, set the environment variable OMP NUM THREADS to 1 unless you know what you are doing. See Sec.3 for more info
on this and on the difference between MPI and OpenMP parallelization.
If you get a mysterious ”too many communicators” error and a subsequent crash: there is
a bug in Intel MPI and MKL 2016 update 3. See this thread and the links quoted therein:
http://www.mail-archive.com/pw_forum@pwscf.org/msg29684.html.
Linux PCs with ACML libraries For AMD CPUs, especially recent ones, you may
find convenient to link AMD acml libraries (can be freely downloaded from AMD web site).
configure should recognize properly installed acml libraries.
19

2.7.6

Linux PC clusters with MPI

PC clusters running some version of MPI are a very popular computational platform nowadays.
Quantum ESPRESSO is known to work with at least two of the major MPI implementations
(MPICH, LAM-MPI), plus with the newer MPICH2 and OpenMPI implementation. configure
should automatically recognize a properly installed parallel environment and prepare for parallel
compilation. Unfortunately this not always happens. In fact:
• configure tries to locate a parallel compiler in a logical place with a logical name, but
if it has a strange names or it is located in a strange location, you will have to instruct
configure to find it. Note that in many PC clusters (Beowulf), there is no parallel
Fortran compiler in default installations: you have to configure an appropriate script,
such as mpif90.
• configure tries to locate libraries (both mathematical and parallel libraries) in the usual
places with usual names, but if they have strange names or strange locations, you will
have to rename/move them, or to instruct configure to find them. If MPI libraries are
not found, parallel compilation is disabled.
• configure tests that the compiler and the libraries are compatible (i.e. the compiler may
link the libraries without conflicts and without missing symbols). If they aren’t and the
compilation fails, configure will revert to serial compilation.
Apart from such problems, Quantum ESPRESSO compiles and works on all non-buggy,
properly configured hardware and software combinations. In some cases you may have to
recompile MPI libraries: not all MPI installations contain support for the Fortran compiler of
your choice (or for any Fortran compiler at all!).
If Quantum ESPRESSO does not work for some reason on a PC cluster, try first if
it works in serial execution. A frequent problem with parallel execution is that Quantum
ESPRESSO does not read from standard input, due to the configuration of MPI libraries: see
Sec.3.4. If you are dissatisfied with the performances in parallel execution, see Sec.3 and in
particular Sec.3.4.
2.7.7

Microsoft Windows

MS-Windows users may compile Quantum ESPRESSO on MinGW/MSYS. Download the
installer from https://osdn.net/projects/mingw/, install MinGW, MSYS, gcc and gfortran.
Start a shell window; run ”./configure”; edit make.inc; uncommenting the second definition
of TOPDIR (the first one introduces a final ”/” that Windows doesn’t like); run ”make”.
Note that on some Windows the code fails when checking that tmp dir is writable, for unclear
reasons.
Another option is Cygwin, a UNIX environment which runs under Windows: see
http://www.cygwin.com/.
Finally, Windows-10 users may enable the Windows Subsystem for Linux and install there
a Linux distribution.
2.7.8

Mac OS

Mac OS-X machines (10.4 and later) with Intel CPUs are supported by configure, both
with gfortran and with the Intel compiler ifort and MKL libraries. Parallel compilation with
20

OpenMPI also works.
Gfortran information and binaries for Mac OS-X here: http://hpc.sourceforge.net/ and
https://wiki.helsinki.fi/display/HUGG/GNU+compiler+install+on+Mac+OS+X.
Mysterious crashes, occurring when zdotc is called, are due to the same incompatibility of
complex functions with some optimized BLAS as reported in the ”Linux PCs with gfortran”
paragraph. Workaround: add preprocessing option -Dzdotc=zdotc wrapper to DFLAGS.

21

3

Parallelism

3.1

Understanding Parallelism

Two different parallelization paradigms are currently implemented in Quantum ESPRESSO:
1. Message-Passing (MPI). A copy of the executable runs on each CPU; each copy lives in a
different world, with its own private set of data, and communicates with other executables
only via calls to MPI libraries. MPI parallelization requires compilation for parallel
execution, linking with MPI libraries, execution using a launcher program (depending
upon the specific machine). The number of CPUs used is specified at run-time either as
an option to the launcher or by the batch queue system.
2. OpenMP. A single executable spawn subprocesses (threads) that perform in parallel specific tasks. OpenMP can be implemented via compiler directives (explicit OpenMP) or
via multithreading libraries (library OpenMP). Explicit OpenMP require compilation for
OpenMP execution; library OpenMP requires only linking to a multithreading version of
mathematical libraries, e.g.: ESSLSMP, ACML MP, MKL (the latter is natively multithreading). The number of threads is specified at run-time in the environment variable
OMP NUM THREADS.
MPI is the well-established, general-purpose parallelization. In Quantum ESPRESSO
several parallelization levels, specified at run-time via command-line options to the executable,
are implemented with MPI. This is your first choice for execution on a parallel machine.
The support for explicit OpenMP is steadily improving. Explicit OpenMP can be used
together with MPI and also together with library OpenMP. Beware conflicts between the various
kinds of parallelization! If you don’t know how to run MPI processes and OpenMP threads in
a controlled manner, forget about mixed OpenMP-MPI parallelization.

3.2

Running on parallel machines

Parallel execution is strongly system- and installation-dependent. Typically one has to specify:
1. a launcher program such as mpirun or mpiexec, with the appropriate options (if any);
2. the number of processors, typically as an option to the launcher program;
3. the program to be executed, with the proper path if needed;
4. other Quantum ESPRESSO-specific parallelization options, to be read and interpreted
by the running code.
Items 1) and 2) are machine- and installation-dependent, and may be different for interactive
and batch execution. Note that large parallel machines are often configured so as to disallow
interactive execution: if in doubt, ask your system administrator. Item 3) also depend on your
specific configuration (shell, execution path, etc). Item 4) is optional but it is very important
for good performances. We refer to the next section for a description of the various possibilities.

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3.3

Parallelization levels

In Quantum ESPRESSO several MPI parallelization levels are implemented, in which both
calculations and data structures are distributed across processors. Processors are organized in
a hierarchy of groups, which are identified by different MPI communicators level. The groups
hierarchy is as follow:
• world: is the group of all processors (MPI COMM WORLD).
• images: Processors can then be divided into different ”images”, each corresponding to a
different self-consistent or linear-response calculation, loosely coupled to others.
• pools: each image can be subpartitioned into ”pools”, each taking care of a group of
k-points.
• bands: each pool is subpartitioned into ”band groups”, each taking care of a group of
Kohn-Sham orbitals (also called bands, or wavefunctions). Especially useful for calculations with hybrid functionals.
• PW: orbitals in the PW basis set, as well as charges and density in either reciprocal or real
space, are distributed across processors. This is usually referred to as ”PW parallelization”. All linear-algebra operations on array of PW / real-space grids are automatically
and effectively parallelized. 3D FFT is used to transform electronic wave functions from
reciprocal to real space and vice versa. The 3D FFT is parallelized by distributing planes
of the 3D grid in real space to processors (in reciprocal space, it is columns of G-vectors
that are distributed to processors).
• tasks: In order to allow good parallelization of the 3D FFT when the number of processors
exceeds the number of FFT planes, FFTs on Kohn-Sham states are redistributed to
“task” groups so that each group can process several wavefunctions at the same time.
Alternatively, when this is not possible, a further subdivision of FFT planes is performed.
• linear-algebra group: A further level of parallelization, independent on PW or k-point
parallelization, is the parallelization of subspace diagonalization / iterative orthonormalization. Both operations required the diagonalization of arrays whose dimension is the
number of Kohn-Sham states (or a small multiple of it). All such arrays are distributed
block-like across the “linear-algebra group”, a subgroup of the pool of processors, organized in a square 2D grid. As a consequence the number of processors in the linear-algebra
group is given by n2 , where n is an integer; n2 must be smaller than the number of processors in the PW group. The diagonalization is then performed in parallel using standard
linear algebra operations. (This diagonalization is used by, but should not be confused
with, the iterative Davidson algorithm). The preferred option is to use ELPA and ScaLAPACK; alternative built-in algorithms are anyway available.
Note however that not all parallelization levels are implemented in all codes.
About communications Images and pools are loosely coupled: inter-processors communication between different images and pools is modest. Processors within each pool are instead
tightly coupled and communications are significant. This means that fast communication hardware is needed if your pool extends over more than a few processors on different nodes.
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Choosing parameters : To control the number of processors in each group, command line
switches: -nimage, -npools, -nband, -ntg, -ndiag or -northo (shorthands, respectively: -ni,
-nk, -nb, -nt, -nd) are used. As an example consider the following command line:
mpirun -np 4096 ./neb.x -ni 8 -nk 2 -nt 4 -nd 144 -i my.input
This executes a NEB calculation on 4096 processors, 8 images (points in the configuration space
in this case) at the same time, each of which is distributed across 512 processors. k-points are
distributed across 2 pools of 256 processors each, 3D FFT is performed using 4 task groups (64
processors each, so the 3D real-space grid is cut into 64 slices), and the diagonalization of the
subspace Hamiltonian is distributed to a square grid of 144 processors (12x12).
Default values are: -ni 1 -nk 1 -nt 1 ; nd is set to 1 if ScaLAPACK is not compiled, it
is set to the square integer smaller than or equal to half the number of processors of each pool.
Massively parallel calculations For very large jobs (i.e. O(1000) atoms or more) or for
very long jobs, to be run on massively parallel machines (e.g. IBM BlueGene) it is crucial to use
in an effective way all available parallelization levels: on linear algebra (requires compilation
with ELPA and/or ScaLAPACK), on ”task groups” (requires run-time option ”-nt N”), and
mixed MPI-OpenMP (requires OpenMP compilation: configure–enable-openmp). Without a
judicious choice of parameters, large jobs will find a stumbling block in either memory or CPU
requirements. Note that I/O may also become a limiting factor.
3.3.1

Understanding parallel I/O

In parallel execution, each processor has its own slice of data (Kohn-Sham orbitals, charge
density, etc), that have to be written to temporary files during the calculation, or to data files
at the end of the calculation. This can be done in two different ways:
• “collected”: all slices are collected by the code to a single processor that writes them to
disk, in a single file, using a format that doesn’t depend upon the number of processors
or their distribution. This is the default since v.6.2 for final data.
• “distributed”: each processor writes its own slice to disk in its internal format to a
different file. The “distributed” format is fast and simple, but the data so produced is
readable only by a job running on the same number of processors, with the same type of
parallelization, as the job who wrote the data, and if all files are on a file system that is
visible to all processors (i.e., you cannot use local scratch directories: there is presently
no way to ensure that the distribution of processes across processors will follow the same
pattern for different jobs). The distributed format for final data requires compilation with
-D__OLDXML preprocessing option and will be removed in the next releases.
The directory for data is specified in input variables outdir and prefix (the former can
be specified as well in environment variable ESPRESSO TMPDIR): outdir/prefix.save. A
copy of pseudopotential files is also written there. If some processor cannot access the data
directory, the pseudopotential files are read instead from the pseudopotential directory specified
in input data. Unpredictable results may follow if those files are not the same as those in the
data directory!
IMPORTANT: Avoid I/O to network-mounted disks (via NFS) as much as you can! Ideally
the scratch directory outdir should be a modern Parallel File System. If you do not have any,
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you can use local scratch disks (i.e. each node is physically connected to a disk and writes to
it) but you may run into trouble anyway if you need to access your files that are scattered in
an unpredictable way across disks residing on different nodes.
You can use input variable disk io to reduce the the amount of I/O done by pw.x. Since
v.5.1, the dafault value is disk io=’low’, so the code will store wavefunctions into RAM and
not on disk during the calculation. Specify disk io=’medium’ only if you have too many kpoints and you run into trouble with memory; choose disk io=’none’ if you do not need to
keep final data files.
For very large cp.x runs, you may consider using wf collect=.false., memory=’small’
and saverho=.false. to reduce I/O to the strict minimum.

3.4

Tricks and problems

Many problems in parallel execution derive from the mixup of different MPI libraries and runtime environments. There are two major MPI implementations, OpenMPI and MPICH, coming
in various versions, not necessarily compatible; plus vendor-specific implementations (e.g. Intel MPI). A parallel machine may have multiple parallel compilers (typically, mpif90 scripts
calling different serial compilers), multiple MPI libraries, multiple launchers for parallel codes
(different versions of mpirun and/or mpiexec). You have to figure out the proper combination
of all of the above, which may require using command module or manually setting environment
variables and execution paths. What exactly has to be done depends upon the configuration
of your machine. You should inquire with your system administrator or user support (if available; if not, YOU are the system administrator and user support and YOU have to solve your
problems).
Always verify if your executable is actually compiled for parallel execution or not: it is
declared in the first lines of output. Running several instances of a serial code with mpirun or
mpiexec produces strange crashes.
Trouble with input files Some implementations of the MPI library have problems with
input redirection in parallel. This typically shows up under the form of mysterious errors when
reading data. If this happens, use the option -i (or -in, -inp, -input), followed by the input
file name. Example:
pw.x -i inputfile -nk 4 > outputfile
Of course the input file must be accessible by the processor that must read it (only one processor
reads the input file and subsequently broadcasts its contents to all other processors).
Apparently the LSF implementation of MPI libraries manages to ignore or to confuse even
the -i/in/inp/input mechanism that is present in all Quantum ESPRESSO codes. In this
case, use the -i option of mpirun.lsf to provide an input file.
Trouble with MKL and MPI parallelization If you notice very bad parallel performances
with MPI and MKL libraries, it is very likely that the OpenMP parallelization performed by
the latter is colliding with MPI. Recent versions of MKL enable autoparallelization by default
on multicore machines. You must set the environment variable OMP NUM THREADS to 1 to
disable it. Note that if for some reason the correct setting of variable OMP NUM THREADS
does not propagate to all processors, you may equally run into trouble. Lorenzo Paulatto (Nov.
25

2008) suggests to use the -x option to mpirun to propagate OMP NUM THREADS to all
processors. Axel Kohlmeyer suggests the following (April 2008): ”(I’ve) found that Intel is now
turning on multithreading without any warning and that is for example why their FFT seems
faster than FFTW. For serial and OpenMP based runs this makes no difference (in fact the
multi-threaded FFT helps), but if you run MPI locally, you actually lose performance. Also
if you use the ’numactl’ tool on linux to bind a job to a specific cpu core, MKL will still try
to use all available cores (and slow down badly). The cleanest way of avoiding this mess is to
either link with
-lmkl intel lp64 -lmkl sequential -lmkl core (on 64-bit: x86 64, ia64)
-lmkl intel -lmkl sequential -lmkl core (on 32-bit, i.e. ia32 )
or edit the libmkl ’platform’.a file. I’m using now a file libmkl10.a with:
GROUP (libmkl_intel_lp64.a libmkl_sequential.a libmkl_core.a)
It works like a charm”. UPDATE: Since v.4.2, configure links by default MKL without
multithreaded support.
Trouble with compilers and MPI libraries Many users of Quantum ESPRESSO, in
particular those working on PC clusters, have to rely on themselves (or on less-than-adequate
system managers) for the correct configuration of software for parallel execution. Mysterious and irreproducible crashes in parallel execution are sometimes due to bugs in Quantum
ESPRESSO, but more often than not are a consequence of buggy compilers or of buggy or
miscompiled MPI libraries.

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