Development of Many-Body Methods for Flame Chemistry and Large Molecule Applications

摘要

Ab initio MBPT and coupled cluster (CC) gradient methods have been developed for studies of potential energy surfaces for molecules. Example calculations include N2H2, SiC2, B2H6 and BH3 and nucleic acid bases among others. Detailed first principle correlated predictions of IR spectra, frequencies and intensities are reported. These methods are used to search for the unknown N3H3 molecule. It is found that it should exist in three stable forms. Detailed IR spectra are provided to aid in its identification. The same methods demonstrate that the currently accepted experimental spectra of the transient BH3 molecule is misinterpreted. Additional work focused on the development and use of MBPT/CC methods in large molecule studies. Methods are developed based upon localized orbitals that should make it possible to study much larger molecules than is currently possible. Other MBPT/CC results are reported for the relative stabilities of nucleic acid bases, particularly cytosine. Such tautomers are important in the theory of point mutations that can lead to tumor formation. It is demonstrated that the effects of electron correlation are crucial in determining accurate energy differences.