I'm modelling a small set of proline analogues - extra functional groups, sulfur in the ring. Using Gaussian / DMACRYS.
--functional B3LYP EmpiricalDispersion=GD3BJ --basis_set 6-311G**
-fun B3LYP EmpiricalDispersion=GD3BJ -bas 6-311G**
Would EmpiricalDispersion=GD3BJ go under -fun, or would it go under
--additional_args? (If so, please show how, I can't get this to run correctly, unsure of the syntax)
To model this more accurately, PBEPBE has been suggested, pure DFT rather than hybrid functional, so there is increased accuracy. Is there a sufficient increase in accuracy for the increase in computational time, or is it better to apply dispersion corrections to B3LYP? (Or PBEPBE and corrections?) Is there another level of theory you would suggest trying?
The electrostatic interactions seem to be over-modelled using B3LYP / 6-311G**, is there a basis set / functional combination (without or with corrections) that would not over-estimate the energy of the + / - charge interactions? (I've tried CAM-B3LYP, but doesn't work on my system.)