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hi all
i am doing geometry relaxation incluing vdw-DF functional , some of following parameters (marked red) needs to be used. but in the manual, i did not find any information about these parameters are constant for all the system and elements or not?

if not , where to find the principle to set these parameters?

thank you !!


for the optB88 functional, or


GGA = MK
PARAM1 = 0.1234
PARAM2 = 1.0000for the optB86b functional.

For the vdW-DF2 functional the rPW86 exchange functional is used:




GGA = ML

moreover, the vdW functional needs to be changed to the vdW2 correlation which requires only a change of a parameter:

Zab_vdW = -1.8867 An overview of the performance

The PARAM1 and PARAM2 are parameters which define the exchange functionals optB88 and optB86b, the Zab_vdW is a parameter which is used in the vdW and vdW2 correlation functionals of Langreth and Lundqvist. They are part of the functionals, independent of the system you study and therefore should not be changed.

The Zab_vdW needs to be set to the -1.8867 value only if you want to use the vdW-DF2 functional. If you want to use the correlation functional of Dion et al. (to do revPBE-vdW, optB88-vdW, or optB86b-vdW calculations) you don't have to specify this parameter.

You can read more details in the references cited from the manual page:
117 for the optB88, 119 for optB86b, and 118 for the vdW-DF2 functional.

thank you very much. i wiil read the mentioned reference!