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I see where MBD and MBD@rsSCS can be called, but I am not clear how one selects (or if one needs to) a base functional like PBE or r2scan. The graphite example only uses IVDW = 20 or 202 but does not use a GGA keyword. How, for example, would I do a PBE+MBD calculation?
Thank you
Dear KWH,
thank you for asking your question in the official VASP forum.
For MBD@rsSCS calculations in VASP you use the normal GGA tag to select the exchange correlation functional. So if you select IVDW=202 you can combine this with any functional available in VASP. However importantly you must set when not using GGA=PBE the value for VDW_SR appropriately. The default is only correct for PBE: wiki/index.php/Many-body_dispersion_energy . On this wiki page are some of the known values listed. I do believe after talking to my colleague that there is no such scaling value yet for r2scan (but it is known for SCAN, see wiki page). You would need to check the literature for a value for r2scan.
Since VASP ver 6.4.3 there is also the option to link the external library libmbd to VASP and use that implementation: wiki/index.php/LIBMBD_METHOD .
So my default your MBD calculation is done using PBE. Otherwise you have to specify the GGA tag + VDW_SR.
Best regards,
Alex H.