AB INITIO CALCULATIONS OF VITAMIN B12 COMPOUNDS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We are developing computations of Raman frequencies and intensities for Ag-cluster-molecule systems and for substituted-cobalamin molecules where vibronic coupling is important. Also we are calculating electronic spectra and bond breaking processes in the substituted-cobalamin molecules. Our plan is to first calculated optimized ground states ( DFT) and excited states (TD-DFT) of cobalamin molecules and the Ag-cluster-molecule systems and to calculate their normal mode coordinates and frequencies, using the Gaussian or ADF package of quantum chemistry programs. We will use the LANL2DZ double zeta basis set at the B3LYP hybrid functional level and/or the BP86 functional with nonlocal correlation and the TZVP basis set. Relative activity of the modes will be compared to relative experimental intensity results. We will calculate and compare both static and dynamic polarizabilities. Then we will calculate resonant Raman intensities using either the ADF or the Dalton quantum chemistry program by taking numerical derivatives of the dynamic polarizability tensor components with respect to the normal mode displacements. For molecules on metal-clusters (nanoparticles) and for substituted-cobalamins, we will calculate excited state potential energy surfaces , dipole transition moments, and oscillator strengths. Finally the effect of vibonic coupling will be investigated by calculating the electronic coupling constants.