# Pseudopotentials and PAW atomic data

### This page gives hints on how to master the use of norm-conserving pseudopotentials and PAW atomic data, and their consequences with the ABINIT package.

##### Copyright (C) 2016-2017 ABINIT group (XG)

Mentioned in topic_AtomTypes, topic_Verification, help_abinit#5, help_features#2.2.

### Table of content:

- 1. Introduction.
- 2. Related lesson(s) of the tutorial.
- 3. Related input variables.

### 1. Introduction.

ABINIT can read many different types of norm-conserving pseudopotentials and PAW atomic data. The names of the files to be used in an ABINIT run are to be provided in the "files" file, one for each type of atom. Note that one cannot mix norm-conserving pseudopotentials with PAW atomic data files in a single ABINIT run, even for different datasets. One has to stick either to norm-conserving pseudopotentials or to PAW.

Norm-conserving pseudopotential tables

There are several sets of norm-conserving pseudopotentials available for most elements of the periodic table, either in LDA or in GGA-PBE. The recommended one (GGA-PBE, ixc=11) comes from the ONCVPSP generator (with spin-orbit coupling). The Goedecker HGH table (LDA, ixc=1, also including spin-orbit coupling) is also available, at https://www.abinit.org/downloads/psp-links/psp-links/hgh. It is rather accurate, but requires often large ecut. The old Troullier-Martins type tables ( LDA ixc=1 and GGA ixc=11) are deprecated, because not accurate enough, and also not including spin-orbit coupling. The different format for norm-conserving pseudopotentials are described in https://wiki.abinit.org/doku.php?id=developers:pseudos.

PAW atomic data tables

Five large sets of PAW atomic data can be read by ABINIT. The recommended one (JTH) for both LDA and GGA-PBE is available on the ABINIT web site PAW page. It uses the PAW-XML format. The links to other sets are provided in the same Web page, see the end of the section "Documents and tools"

Validation

Many pseudopotentials (norm-conserving as well as PAW) have been tested against all-electron calculations, see the section "Documents and tools" paragraph about the "Delta" project on the ABINIT web site PAW page. In paw3 it is explained How to perform more detailed comparisons with an all-electron code.

Generation

Six codes are available to generate new pseudopotentials when needed, see the related ABINIT web page. For norm-conserving pseudopotentials, ONCVPSP is the preferred one. The ultra-soft pseudopotentials generated by "USPP" are approximations of the Projector Augmented Wave approach, and are treated within the PAW framework in ABINIT. The ATOMPAW generator is actually tightly connected to ABINIT such that there are ABINIT automatic tests in which a PAW atomic data is generated, and then used in ABINIT. There is also a dedicated tutorial to ATOMPAW/ABINIT.

Miscellaneous

Norm-conserving pseudopotentials can be mixed, to generate "alchemical" pseudoatoms, see topic_AtomTypes.
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### 2. Related lesson(s) of the tutorial.

- Second lesson on the projector-augmented wave technique The generation of atomic data.
- Third lesson on the projector-augmented wave technique Testing PAW datasets against an all-electron code.
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  ### 3. Related input variables.

  Compulsory input variables:

  ... ntypat [Number of TYPes of AToms]
  ... znucl [charge -Z- of the NUCLeus]

  Relevant internal variables:

  ... %ziontypat [Z (charge) of the IONs for the different TYPes of AToms]

  Input variables for experts:

  ... npsp [Number of PSeudoPotentials]
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