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[[Category:Software]][[Category:ComputationalChemistry]]

__NOTOC__
:"''Quantum ESPRESSO is an integrated suite of Open-Source computer codes for electronic-structure calculations and materials modeling at the nanoscale. It is based on density-functional theory, plane waves, and pseudopotentials.''
:[...]

:''Quantum ESPRESSO has evolved into a distribution of independent and inter-operable codes in the spirit of an open-source project. The Quantum ESPRESSO distribution consists of a “historical” core set of components, and a set of plug-ins that perform more advanced tasks, plus a number of third-party packages designed to be inter-operable with the core components.''<ref>[http://www.quantum-espresso.org/ Quantum ESPRESSO web site].</ref>

= Usage =
To use Quantum ESPRESSO, you need to load a module (see [[Utiliser des modules/en|Using modules]]). You can see available versions using <code>module avail quantumespresso</code> or <code>module spider quantumespresso</code>, and load one with (for example), <code>module load quantumespresso/6.6</code>.

{{File
  |name=qe_ex1.sh
  |lang="sh"
  |contents=
#!/bin/bash
#SBATCH --account=def-someuser
#SBATCH --time=0-1:00           # DD-HH:MM
#SBATCH --nodes=1
#SBATCH --tasks-per-node=32     # MPI tasks
#SBATCH --mem=0                 # all memory on node
module load StdEnv/2020  intel/2020.1.217  openmpi/4.0.3
module load quantumespresso/6.6
srun pw.x < si.scf.in > si.scf.out 
}}

The above example requests 32 processes, which is more than needed for the silicon tutorial case. Please be aware that suitable selection of a process count is complicated, but it is your responsibility to choose an efficient number.  See also [[Advanced MPI scheduling]].

= Known problems =

== No pseudopotential files ==
There is no system-wide repository of pseudopotentials for Quantum ESPRESSO on our clusters. You must find or create and store your own pseudopotential files.

== Segfaults with OpenMPI 3.1.2 ==

Users have reported random segfaults on Cedar when using Quantum ESPRESSO versions compiled for OpenMPI 3.1.2 in single-node jobs (shared memory communication). These issues seem not to happen with other versions of OpenMPI. If you experience such problems, first try to use an OpenMPI 2.1.1-based toolchain. For example:

{{Commands
|module load gcc/5.4.0
|module load openmpi/2.1.1
|module load quantumespresso/6.3
}}

== Parameter error in Grimme-D3 ==

Incorrect results may be obtained when running Grimme-D3 with the element barium (Ba).
The error comes from an incorrect value for one of the coefficients for barium,
specifically, the r2r4 parameter in the source code file <code>dft-d3/core.f90</code>. 
The correct value should be 10.15679528, not 0.15679528.  
The error has been confirmed by the QE developers to exist in all versions from 6.2.1 to 7.1.
<ref>[https://www.mail-archive.com/users@lists.quantum-espresso.org/msg42277.html "Wrong r2r4 value for Ba in the dft-d3 code", Quantum ESPRESSO mailing list, 2022 July 9].</ref>