Available pseudopotentials: Difference between revisions

Revision as of 13:51, 16 October 2023

Projector augmented wave (PAW) potentials are available for all elements in the periodic table from the VASP Portal. These are for the PAW method and are stored in POTCAR files. The distributed PAW potentials have been generated by G. Kresse following the recipes discussed in ^[1], whereas the PAW method has been first suggested and used by Peter Blöchl ^[2]. Therefore, if you use any of the supplied PAW potentials, you should include these two references.

Except for the 1st-row elements, all PAW potentials are designed to work reliably and accurately at an energy cutoff of roughly 250 eV. This is a key aspect of making the calculation computationally cheap. The default energy cutoff is set by the ENMAX tag in the POTCAR file.

Why to use PAW potentials

Generally, the PAW potentials are more accurate than ultra-soft pseudopotentials (US-PP). There are two reasons for this: First, the radial cutoffs (core radii) are smaller than the radii used for US-PP. Second, the PAW potentials reconstruct the exact valence wavefunction with all nodes in the core region. Since the core radii of the PAW potentials are smaller, the required energy cutoffs and basis sets are also larger. If such high precision is not required, the older US-PP can be used in principle, but it is discouraged. This is because the energy cutoffs have not changed appreciably for C, N, and O. Thus, the increase in the basis-set size will usually be small so that calculations for compounds that include any of these elements are not more expensive with PAW than with US-PP.

Different versions

For most elements different versions of PAW potentials exist within a specific release (e.g. potpaw_PBE.54). The different POTCAR files can be destinguished by the following suffixes:

suffix	explanation	example
_pv	semicore p states are considered valence states	The Ti potential has four valence electrons, two in the 3d shell, and two in the 4s shell. Ti_pv adds 6 electrons in the 3p shell.	_sv	semicore s states are considered valence states	}

[kresse:prb:99-1] I. G. Kresse and D. Joubert, Phys. Rev. B 59, 1758 (1999).

[bloechl:prb:94b-2] P. E. Blöchl, Phys. Rev. B 50, 17953 (1994).

[1]

[2]

@@ Line 14: / Line 14: @@
 {| class="wikitable"
 |-
-| suffix	|| explanation
+| suffix	|| explanation || example
 |-
-|'''_pv''' 	|| semicore ''p'' states are considered valence states
+|'''_pv''' 	|| semicore ''p'' states are considered valence states || The Ti potential has four valence electrons, two in the ''3d'' shell, and two in the ''4s'' shell. Ti_pv adds 6 electrons in the ''3p'' shell.
-|}
+|'''_sv''' 	|| semicore ''s'' states are considered valence states || Ti_sv adds 2 more electrons, so now we have a <math>3s^23p^63d^24s^2</math> configuration with 12 total electrons|}