Pseudopotentials supplied with the VASP package

VASP is supplied with a set of standard pseudopotentials (PP), and we urge all VASP users to use this set of PP or the novel PAW potentials (see Sec. 10.2). The pseudopotentials are located at our file server: (see also section 3.2):

x
  cms.mpi.univie.ac.at:~vasp/pot/potcar.date.tar
  cms.mpi.univie.ac.at:~vasp/pot_GGA/potcar.date.tar

It was a difficult and time-consuming task to generate these PP's. The reasoning for their generation is, however, obvious. PP generation was, and still is, a tricky, cumbersome, error-prone and time-consuming task, and only few groups can afford to generate a new PP for every problem at hand. But, if a large user community applies the same set of pseudopotentials to widely different problems, ill-behaved PP are easily spotted and can be replaced by improved potentials.

This philosophy has certainly paid of. The PP's supplied with VASP are among the best pseudopotentials presently available, but the pseudopotential method has been superceded by better electronic structure methods, such as the PAW method. Hence, the development of the pseudopotentials distributed has come to an end, and we strongly recommend to use the PAW datasets now supplied in the VASP-PAW package (see Sec. 10.2).

All supplied PP's with VASP are of the ultra soft type (with few exceptions). And for most elements only one LDA and one GGA PP is supplied. All pseudopotentials are supplied with default cutoffs (lines ENMAX and ENMIN in the POTCAR files), and information on how the PP was generated. This should make it easier to determine which version was used, and user mistakes are easier to correct. The POTCAR files also contain information on 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 requires a correction for the spin-polarization energies of the atoms.

For the transition metals an additional problem exists: The cohesive energies written out by VASP are with respect to a "virtual" non spin-polarized pseudo-atom having one s electron and N valence-1 d electrons. This is usually 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, using the procedure described in Sec. 9.5.

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 related to deficiencies of the LDA/GGA approximation. Only configuration interaction (CI) calculations are presently able to predict the groundstate of all transition metals correctly.

Table 4: Correction to the energy of the atom for the US-PP. Add this value to the energies determined by VASP.

3d	Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu
exp.	3d 4s2	3d2 4s2	3d3 4s2	3d5 4s	3d5 4s2	3d6 s2	3d7 4s2	3d8 4s2	3d10 4s1
GS	3d 4s2	3d3 4s	3d4 4s	3d5 4s	3d5 4s2	3d6.2	3d7.7	3d9 4s	3d10 4s1
						4s1.8	4s1.3
d(E)
GGA	1.78	2.24	3.77	5.87	5.62	3.15	1.43	0.55	0.22
LDA	1.73	1.99	3.38	5.30	5.02	2.82	1.28	0.49	0.18
4d	Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd
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
d(E)
GGA	1.91	1.91	3.08	4.61	3.06	1.96	1.06	1.51
LDA	1.90	1.66	2.70	4.09	2.73	1.74	0.94	1.46
5d		Hf	Ta	W	Re	Os	Ir	Pt
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
d(E)
GGA		3.05	3.24	4.53	4.42	2.53	0.87	0.48
LDA		2.98	3.10	4.00	4.07	2.33	0.92	0.41

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 this is the reason why cohesive energies do not decrease 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 parameters

in the POTCAR file. We want to point out, that the RRKJ kinetic energy is usually very accurate and corrects for more than $90 \%$ 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$\to$d or s$\to$p).