Available pseudopotentials: Difference between revisions

Revision as of 14:41, 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
_s	This suffix indicates a "softer" potential, with a higher core radius and a lower requirement for the plane-wave energy cutoff. Significant advantages in computation time is achieved at some cost of transferability and accuracy.	The O potential has a core radius of 1.52 atomic units (a.u.) and ENMAX of 400 electron Volts (eV). The O_s potential has a core radius of 1.85 a.u. and a cutoff of 282.9 eV.
_h	This suffix indicates a "harder" potential, with a smaller core radius and a higher requirement for the plane-wave energy cutoff. This type of potentials increases computational cost, but can be necessary, especially if short bonds are present.	The O_h potential has a core radius of 1.1 a.u. and a cutoff of 765.5 eV.
_pv	Semicore $p$ states are considered valence states. Additionally these type of potentials are a bit harder. Computational cost increases, but accuracy and transferability as well.	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 $p$ and $s$ states are considered valence states. Additionally these type of potentials are harder than those without a suffix. Computational cost increases, but accuracy and transferability as well.	Ti_sv adds 2 more electrons, so now we have a $3s^23p^63d^24s^2$ configuration with 12 total electrons
_d	Semicore $d$ states are considered valence states. Additionally these type of potentials are a bit harder. Computational cost increases, but accuracy and transferability as well.	The Ge potential has four valence electrons, two in the $4s$ shell, and two in the $4p$ shell. Ge_d adds 10 electrons in the $3d$ shell.
_2 or _3	Pseudopotentials with an integer suffix denote a specific valence state. These potentials are only provided for the Lanthanides. Some $4f$ electrons for these potentials are put in the frozen core, although they are higher in energy than other valence states. Be careful when using these potentials and read the corrsponding section beforehand	The Er potential has 22 valence electrons with the configuration $4f^{12}5s^25p^66s^2$ and an energy cutoff of ~350 eV. Er_2 has 8 valence electrons with the configuration $5p^66s^2$ and a recommended cutoff energy of ~120 eV, while Er_3 has 9 valence electrons and the configuration $5p^65d^16s^2$ and a cutoff of 155 eV.

[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]

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 |'''_d''' 	|| Semicore <math>d</math> states are considered valence states. Additionally these type of potentials are a bit harder. Computational cost increases, but accuracy and transferability as well.|| The Ge potential has four valence electrons, two in the <math>4s</math> shell, and two in the <math>4p</math> shell. Ge_d adds 10 electrons in the <math>3d</math> shell.
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-|'''_2''' or '''_3''' 	|| Pseudopotentials with an integer suffix denote a specific valence state. These potentials are only provided for the Lanthanides. Some <math>4f</math> electrons for these potentials are put in the frozen core, although they are higher in energy than other valence states. Be careful when using these potentials and read section [[Available_PAW_potentials#Lanthanides]] beforehand || The Er potential has 22 valence electrons with the configuration <math>4f^{12}5s^25p^66s^2</math> and an energy cutoff of 346.3 eV. Er_2 has 8 valence electrons with the configuration <math>5p^66s^2</math>, while Er_3 has 9 valence electrons and the configuration <math>5p^65d^16s^2</math>
+|'''_2''' or '''_3''' 	|| Pseudopotentials with an integer suffix denote a specific valence state. These potentials are only provided for the Lanthanides. Some <math>4f</math> electrons for these potentials are put in the frozen core, although they are higher in energy than other valence states. Be careful when using these potentials and read [[Available_PAW_potentials#Lanthanides|the corrsponding section]] beforehand || The Er potential has 22 valence electrons with the configuration <math>4f^{12}5s^25p^66s^2</math> and an energy cutoff of ~350 eV. Er_2 has 8 valence electrons with the configuration <math>5p^66s^2</math> and a recommended cutoff energy of ~120 eV, while Er_3 has 9 valence electrons and the configuration <math>5p^65d^16s^2</math> and a cutoff of 155 eV.
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