Two versions of PP, which one should be used

For H three POTCAR files exist. The H/POTCAR and H_200eV/POTCAR files actually contain the same PP. The only difference is that H_200eV has a lower default energy cutoff of 200 eV (the default cutoff for H is 340 eV). Up to now we have not found any difference between calculations using 200 and 340 eV, we therefore recommend to use only H_200eV (differences for the $H_2$ dimer are for instance less than $1 \%$). If H is used together with hard elements like carbon VASP will anyway adopt the higher default cutoff of C. The third potential H_soft (generated by J. Furthmueller) should be used in conjunction with soft elements like Si, Ge, Te etc. As one can see from the data_base file H$_2$ dimer length and vibrational frequencies are still quite reasonable.

For the first row elements two PP exist, we recommend the standard version, which gives very high accuracy. The second set ( B_s,C_s,O_s,N_s,F_s) is significantly softer and should be used only after careful testing. We have found that the second set is safe if a hard species is mixed with a softer one (that is for instance the case in Si-C, Si-O$_2$, or even Ti-O$_2$).

For Ga, In, Sn and Pb one should describe the 3d or 4d states as valence, corresponding PP can be found on the server in the directories

    Ga_d, In_d, Sn_d, Pb_d

If one puts the 3d or 4d states in the core the results depend strongly on the location of the position of the d-reference energy. The d-reference energy for the conventional Ga, In, Sn and Pb PP (with d in the core) has been adjusted so that the equilibrium volume is within 1 percent of the equilibrium volume for the Ga_d, In_d and Sn_d PP. This is clearly a ad hoc fix, but results in reasonably accurate pseudopotentials. Mind that PP including d are currently missing for Ge, and for very accurate calculations such a PP might be required.

The following PP are currently available with p semi-core states

    Li_pv
    Na_pv  Mg_pv
    K_pv   Ca_pv Sc_pv Ti_pv V_pv        Fe_pv 
    Rb_pv  Sr_pv Y_pv  Zr_pv Nb_pv Mo_pv
    Cs_pv  Ba_pv             Ta_pv W_pv

For a few elements harder NC-PP exist which can be used in calculations under pressure, for ionic systems, or for oxides:

    Na_h Mg_h Al_h Si_h