quantum-espresso/upflib

Library of pseudopotential code

This directory contains the "upflib" library of pseudopotential-related code, extracted from the Quantum ESPRESSO distribution. This library depends only upon module mp.f90 of UtilXlib and upon a few modules and routines of devXlib; upon a few LAPACK routines; requires a suitable ../make.inc file in Makefile. Other than this, it can be independently compiled.

Currently, upflib includes

• basic definitions of the UPF (Unified Pseudopotential File) format
• basic I/O operations on UPF files
• setup of the interpolation tables and of other basic variables
• interpolation of pseudopotentials
• generation of various pseudopotentials matrix elements
• utilities: spherical harmonics and Bessel functions, integration routines

The available information on pseudopotential formats can be found here: https://gitlab.com/QEF/q-e/-/wikis/Developers/Format-of-pp-files

In addition to the libupf.a library, executable utilities are produced:

• upfconv.x, converting pseudopotentials in other formats into UPF: see upfconv.x -h for more

• virtual_v2.x, courtesy Jingyang Wang (jw598@cornell.edu), generates an averaged pseudopotential suitable for Virtual Crystal Approximation

• casino2upf.x, courtesy Mike Towler (see below)

A python script fixfile.py is also present, to remove undesired & characters from UPF files that hinder their parsing by xml tools.

CASINO and QE pseudopotentials

The following notes are kept for reference (they might be obsolete). Code upfconv.x -c should replace code upf2casino2.x mentioned below. Code casino2upf.x was moved to upflib/ and works (?) again, at least for the example provided by Jake Muff, since v.6.8. Old notes start here:

Two utilities are provided with the Quantum Espresso distribution to enable the PWscf code to be used in conjunction with the CASINO quantum Monte Carlo code.

Of course all pseudopotentials generated via these automatic tools should be tested before being used for production runs.

It should be noted that ultrasoft and PAW pseudopotentials cannot be used with the CASINO code. Currently only UPF files containing norm-conserving pseudopotentials can be converted using these utilities.

casino2upf.x

The first of these is casino2upf.x . This utility takes a given CASINO tabulated pseudopotential file and one or more awfn.data files specifying the pseudoatomic wavefunctions to be used in creating the Kleinman-Bylander projectors. A UPF file containing the projectors and the local potential is then written to the file name specified in inputpp. Any errors are communicated to the user via stderr.

Usage:

    ./casino2upf.x < inputpp

A sample inputpp file for converting a Trail and Needs pseudopotential would be:

inputpp:
	&inputpp
		pp_data='pp.data'
		upf_file='my_pseudo_potential.UPF'
	/
	3
	awfn.data_s1_2S
	awfn.data_p1_2P
	awfn.data_d1_2D

Here pp_data specifies the name and location of the file containing the CASINO pseudopotential. The utility then expects an input card after &inputpp consisting of the number of awfn.data files supplied (in this case 3) and then their names. The files are searched sequentially so the first s wavefunction found will be used for the s projector, first p for the p projector and so on.

A note on the radial grid

The utility currently performs no interpolation and attempts to use the same radial grid as the original pseudopotential. It therefore assumes that the grid will be of the standard form used by Trail and Needs.

If this is not the case the flag tn_grid=.false. can be set in the input file. The standard logarithmic form, r(i)=exp(xmin + i*dx) / Z is then assumed. Values for xmin and dx can also be specified in the input file in the usual way.

If interpolation from a different non-standard grid is required then the current recommended route is to use the casino2gon utility supplied with the CASINO distribution. This produces the older GON format that is (currently) still read by PWscf.

Ghost states

The Kleinman-Bylander form can unfortunately introduce ghost states into some calculations. If this does occur we recommend that the pseudopotential is re-converted using a different local channel. The local channel can be specified in the original CASINO pp.data file and is read in automatically by casino2upf.x .

up2casino.x

This utility takes a standard UPF pseudopotential from standard input and writes a CASINO tabulated pseudopotential file to standard output. Any errors are communicated via stderr.

Usage:

./up2casino.x < pseudo.UPF > pp.data

Care must be taken that the resulting pseudopotential file spec fies the required local channel. Also this utility should only be used with norm-conserving pseudopotentials.