| 10:28:10 AM PST - Fri, Dec 11th 2015 |
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Thank you for the suggestions.
It does make sense to use a range-separated functional, especially for larger distances. I wanted to test if it would make any difference in shorter separation distances as well, so i ran again the simulations with 1.8A separation and the CAM-B3LYP popular range-separated functional.
H2.png
The results are quite similar: basis sets with diffuse functions give much slower oscillations; extrapolating from aug-cc-pVTZ results we would expect a charge oscillation at about 200THz. Is there any chance that non-diffuse basis sets would also converge to that limit, if one could perform cc-pV6Z simulations? In other words, is it better to perform that kind of simulations with diffuse basis sets, since they seem to converge faster?
Also, i noticed an overshooting/undershooting with aug-cc-pVTZ basis set, i.e. not only the excess charge is transfered, but also a small portion of valence charge as well. Does this type of charge transfer has a physical meaning, or it is just an artifact that should be ignored? I have also observed the same kind of overshooting with charge oscillations in O2 dimer with 2A separation. I think, that happens when the separation distance is relatively small. Strange enough, in this example, the largest basis sets aug-cc-pVDZ and cc-pVTZ do not give a complete oscillation:
O2.png
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