Available pseudopotentials: Difference between revisions

From VASP Wiki
Line 4: Line 4:
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 {{TAG|ENMAX}} tag in the [[POTCAR]] file.
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 {{TAG|ENMAX}} tag in the [[POTCAR]] file.


==Why VASP uses PAW potentials==
==Why VASP recommends 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.
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.

Revision as of 09:02, 17 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 VASP recommends 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 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 shell, and two in the shell. Ti_pv adds six electrons in the shell.
_sv Semicore and 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 two more electrons, so now we have a configuration with 12 total electrons
_d Semicore 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 shell, and two in the shell. Ge_d adds ten electrons in the shell.
_2 or _3 Pseudopotentials with an integer suffix denote a specific valence state. These potentials are only provided for the Lanthanides. Some 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 and an energy cutoff of ~350 eV. Er_2 has 8 valence electrons with the configuration and a recommended cutoff energy of ~120 eV, while Er_3 has 9 valence electrons and the configuration and a cutoff of ~155 eV.
_AE These potentials are only provided for H, He, and Li. They are very hard and contain all electrons (AE). SOME MORE WORK NEEDED HERE, ESPECIALLY FOR THE DIFFERENCE BETWEEN Li_sv_GW and Li_AE_GW! Both the He and the HE_AE pseudopotentials contain two electrons, but he _AE variant has an extremely small core radius of 0.6 a.u. (compared to 1.1 a.u. for He), and ENMAX of ~2135 eV.
_GW These potentials are optimized for calculations by using different projectors and taking care to reproduce the all-electron scattering properties for energies far above the Fermi level. They are superior for excited state properties and any calculation considering like RPA, BSE, and MP2. There are some results that indicate that the GW potentials are also more accurate for standard DFT calculations[3], but the results should be very comparable with the standard potentials in most cases. Note that the _GW suffix is often combined with other suffixes. The Ge and the Ge_GW potential do not differ in core-radius, recommended plane-wave-energy cutoff, or the reference configuration of the atom. However, the projectors are different.

List of all DFT-PAW potentials

Please consult the list of all available DFT-PAW potentials, except hydrogen like potentials with fractional valence.

List of all GW/RPA-PAW potentials

Please consult the list of all available GW/RPA-PAW potentials that have been optimized for accurate scattering properties in the high-energy range.

Further recommendations regarding PAW potentials

Hydrogen like potentials with fractional valence

First row elements

Alkali and alkali-earth elements (simple metals)

p-elements

d-elements

f-elements

Lanthanides with fixed valence