PC GAMESS-related discussion club

Re: Week interactions and levels of theory

Alex Granovsky
gran@classic.chem.msu.su


Hi,

I would suggest you to try to optimize your system using PBE0 functional first. PBE0 is considered to be one of the best functionals available for systems with weak interactions. If it fails, then you have no choice but to use either UMP2 or ROMP2. Unfortunately, at moment PC GAMESS lacks open-shell MP2 gradients capabilities. They will be added as a result of our current work on large-scale parallel MP2 gradient program, however, this will certainly take considerable amount of time to implement.

Best regagds,
Alex Granovsky


On Mon Oct 23 '06, Solntsev Pasha wrote
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>Dear PC Gamess users.
>I am going to do geometry optimization of the molecule contained copper(II) ion and two organic moieties interacting one with another. Such interaction is very week and implementation of very large basis set such as 6-31++G(3df3p) does not produce correct and accurate results. Nevertheless, introduction of the MP2 correction were shown to be able to solve this problem. Of course, I cannot use RHF function in that case; on the other hand, MP2 gradient is also unavailable under ROHF(UHF). What is the level of theory should I use due to perform molecule optimization? Are there any routine procedures for such cases? Best regards.
>

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