VASP is supplied with a set of standard PP. Please use our standard pseudopotentials (PP) located at the ftp server (see also section 3.2).
tph.tuwien.ac.at:~vasp/pot/potcar.date.tar tph.tuwien.ac.at:~vasp/pot_GGA/potcar.date.tarIt is not easy to create PP for all elements, the basic idea behind this standard set of PP is to reduce waste of time. If someone finds that one of the PP's is not satisfactory, we can regenerate it. If you are not using these PP you are at your own risk.
All supplied PP are ultra soft. And for most elements only one LDA and one GGA PP is supplied. All pseudopotentials are supplied with a default cutoff (lines ENMAX and ENMIN in the POTCAR files), and information how the PP was generated. This makes it easier to find out which version has been used, and to correct for possible errors. The POTCAR files also contain an information about the energy of the atom in the reference configuration (i.e. the configuration for which the PP was generated). Cohesive energies calculated by vasp are with respect to this configuration. Mind that the cohesive energies written out by vasp require a correction for the spin-polarization energies of the atoms.
For the transition metals there is one additional problem: The cohesive energies written out by VASP are with respect to an "virtual" non spin-polarized pseudo-atom having one s electron and n-1 d electrons, this is NOT the experimental ground state configuration.
The table below gives the required energy corrections (d(E)) for transition metals: i.e. it contains the difference between the "virtual" non spin-polarized pseudo-atom and a spin-polarized groundstate (GS) atom calculated with VASP. The calculations have been done consistently with VASP.
Mind that LDA/GGA is not able to predict the correct groundstate (line exp.) for all transition metals. This is NOT a failure of VASP but one of the LDA/GGA approximation. Only configuration interaction (CI) calculations are at the moment able to predict the groundstate of all transition metals correctly.
|exp.||3d 4s2||3d2 4s2||3d3 4s2||3d5 4s||3d5 4s2||3d6 s2||3d7 4s2||3d8 4s2|
|GS||3d 4s2||3d3 4s||3d4 4s||3d5 4s||3d5 4s2||3d6.2||3d7.7||3d9 4s|
|exp.||4d 5s2||4d2 5s2||4d4 5s||4d5 5s||4d5 5s2||4d7 5s||4d8 5s||4d10|
|GS||4d 5s2||4d3 5s||4d4 5s||4d5 5s||4d5 5s2||4d7 5s||4d8 5s||4d10|
|exp.||5d2 6s2||5d3 6s2||5d4 6s2||5d5 6s2||5d6 6s2||5d9||5d9 6s|
|GS||5d2 6s2||5d3 6s2||5d5 6s||5d5 6s2||5d6 6s2||5d8 6s1||5d9 6s|
The POTCAR file also contains information about the approximate error according to the RRKJ (Rappe, Rabe, Kaxiras and Joannopoulos) kinetic energy criterion. This approximate error is taken into account when cohesive energies are calculated, and because of this it is no longer the case that the cohesive energy decreases strictly with the energy cutoff. If you do not like this feature remove the lines after
Error from kinetic energy argument (eV)till (but not including) the line
END of PSCTR-control parametersin the POTCAR file. We want to point out, that the RRKJ kinetic energy is usually very accurate and corrects for more than of the error in the cohesive energy, but it works only if there is not a considerable charge transfer from one state to another state (s d or s p).