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12.1 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 tex2html_wrap_inline5169 dimer are for instance less than tex2html_wrap_inline5153 ). 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 tex2html_wrap_inline5141 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 save if a hard species is mixed with a softer one (that is for instance the case in Si-C, Si-O tex2html_wrap_inline5141 , or even Ti-O tex2html_wrap_inline5141 ).

For In, Sn and Ga 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 for the Ga_d, In_d and Sn_d PP. This is clearly a fix, but results in reasonable 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

    K_pv   Ca_pv Sc_pv Ti_pv V_pv        Fe_pv 
    Rb_pv        Y_pv  Zr_pv Nb_pv Mo_pv
    Cs_pv
Further PP with semi-core states are planed for transition metals (especially for the 3d-transition metals, like Sr, W etc.).

For a few elements harder NC-PP exist which should be used in calculations under pressure and for ionic systems (usually one does not need semi-core states for these elements and the harder NC-PPs are an cost efficient alternative):

    Na_h Mg_h Al_h Si_h

Some PP are probably still not perfect: Notably one might need PP with p-semi core states for Li, Be, Na and Mg, and for none of the PPs the lower lying s states have been unfrozen (the reason for that is that the current version of the PP generation program does not handle such cases).


next up previous contents
Next: 13 The pseudopotential generation Up: 12 Pseudopotentials supplied with Previous: 12 Pseudopotentials supplied with

MASTER USER VASP
Mon Mar 29 10:38:29 MEST 1999