Ceilidh ... Re: optimal methodology for the calculation of UV spectra of aromatics

PC GAMESS/Firefly-related discussion club

Re: optimal methodology for the calculation of UV spectra of aromatics

>I'm a bit familiar with the use of QM methods in chemistry, but have little practical experience with calculations other than simple geometry optimizations, thus a general request for advice to the members of this forum. I would like to calculate UV absorption maxima, as well as oxidation potentials for a number of aromatic compounds in polar organic solutions; simple examples would be anisol or diphenyl, up to maybe 20-24 C, N, O, S atoms.
>Are there good examples, papers, tutorials or presentations of the proper steps and approaches, preferably with examples of input files, that use a recent version of PC GAMESS/Firefly? Although I've been googling quite a bit, so far I've found just one relevant example: page 32 of Marek Checinski's tutorial on this web site--and the not-so-promising Enrico-Alex exchange on Mon, Mar 31, '08... What methods or theory level would be appropriate to expect a +/-20 nm agreement with exp. spectra?

Typical methods used for excited states of large (50-100 atoms) molecules are TD DFT and CIS. An experienced user can try MCSCF/MCQDPT2. On the other hand, EOM-CC methods (not implemented in Firefly) are good for small (up to 20 atoms) molecules. A good review of single-excitation methods (TD DFT and CIS) is presented in http://pubs.acs.org/doi/abs/10.1021/cr0505627

Fri Jan 16 '09 0:34am

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