The CH_2OH~+→CHO~++H_2 decomposition mechanism: a G3, G3B3, CBS-Q, CBS-QB3 versus pure DFT comparison: interesting variations

摘要

It was reported [J. Mol. Struct (Theochem) 425 (1998) 193] that density functional theory was able to reproduce experimental data for the CH_2OH~+ → CHO~++H_2 decomposition mechanism to above a 5% bar of error. However, the computationally expensive density functional theory methods (coupled to very large basis sets) do not singularly provide these results, thus many theoretical methods must be used to achieve (i.e. HFB, SVWN, B3LYP, B3PW91, etc.) results that correlate well with known quantities. This many not be practical for experimental purposes. Newly implemented methods such as CBS-Q, CBS-QB3, G3 and G3B3 allow a very fast approximation to very high level ab initio methods such as QCISD (T) with a fraction of the time. Also, a comparison of not only geometrical affects between wave function based MP2 optimizations and the B3LYP optimization is possible (X versus XB3, where X = CBS-Q or G3) but also basis set affects can be explore to some extent. The results of the CBS-Q, CBS-QB3, G3 and G3B3 calculations for the singlet cationic decomposition potential energy surface of CH_2OH_+ will be presented.