QE PW Input File

This page explains the PW input files in more detail. It refers to each of the examples and the input files auto-generated by each of the scripts.

A standard PW file contains options for the locations of associated files, and any output files, as well any information about the system, including the atoms and their positions, and the dimensions of the cell. For users new to Quantum Espresso, it is often easier to copy working PW files and editing individual parameters rather than building these from scratch. For those that are interested, there are also tools that generate PW input files, such as ASE [1]. Alternatively a number of users have written their own helper scripts to expedite the tedious procedure of creating large batches of input files for larger investigations.

An essential reference page is the PW input file description page [2], which contains a brief explanation of every possible choice of parameter and their options.

Example 1

The input file generated for the first example is for an isolated water molecule chosen to be the system. Isolation is imposed by Environ, so although there are options on the Quantum-Espresso side (see Example 3), these are not necessary here. We start at the bottom of the file with the definition of the water molecule. Quantum Espresso expects the initial positions of the water in some consistent reasonable choice of units.

ATOMIC_SPECIES
 H   1  H.pbe-rrkjus.UPF
 O  16  O.pbe-rrkjus.UPF
ATOMIC_POSITIONS (bohr)
O   11.79  12.05  11.50
H   13.45  11.22  11.50
H   10.56  10.66  11.50

The atomic species keyword introduces each individual atom present in the system, along with their atomic mass and the name of the pseudopotential file they should refer to. Note that Quantum Espresso can have multiple entries of the same atomic species (which should be labelled differently). The pseudopotential files should be placed in a folder referenced by the pseudopotential directory choice (whose default can be set in the environment variables for Quantum Espresso, or manually set as we will show here in the input file).

[1]	https://wiki.fysik.dtu.dk/ase/index.html

[2]	https://www.quantum-espresso.org/Doc/INPUT_PW.html