AB INITIO CALCULATIONS OF VITAMIN B12 COMPOUNDS

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 我们想要计算开壳维生素B12(钴胺)分子的性质和表面分子的拉曼光谱强度。在这两种情况下，Born-Oppenheimer近似的崩溃都会导致振子相互作用，从而扭曲钴胺分子的几何结构(PJT效应)或改变表面分子的相对拉曼强度。我们将使用CASSCF方法计算钴胺分子的性质；然而，我们将投资使用TD-DFT的其他可能的方法，那里的计算更有效。我们将用从头算方法计算拉曼强度，该方法应该同时包括Franck-Condon和Herzberg-Teller类型的共振拉曼散射。这一方法将用于了解表面增强拉曼散射(SERS)的基本增强机制。这一计算将对银纳米簇上的吡啶和3-羟基黄酮类化合物进行。一种可能的计算方法包括使用多组态CASSCF波函数的耦合微扰Hartree-Fock方程(CPHF)的高斯程序包来获得随频率变化的极化率分量。然后，通过计算动态极化率的数值导数作为所有原子相对于平衡几何的笛卡儿位移的函数，从微分散射截面得到拉曼散射强度。这种计算的其他方法将在量子化学的ADF或MOLPRO程序包中进行研究。

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 would like to calculate properties of open-shell vitamin B12 (cobalamin) molecules and the intensities of the Raman spectroscopy for molecules on surfaces. In both cases a break down in the Born-Oppenheimer approximation can lead to vibronic interactions which distorts the molecular geometry ( PJT effect) for cobalamins or changes the relative Raman intensities for molecules on surfaces. We will calculate the properties of cobalamin molecules using the CASSCF method ; however , we will be investing other possible approaches using TD-DFT where the computation is more efficient. We will calculate Raman intensities by an ab initio method which should include both Franck-Condon and Herzberg-Teller type resonance Raman scattering. This approach will be used in order to obtain an understanding of the basic enhancement mechanisms of Surface Enhanced Raman Scattering (SERS). This calculation will be made for pyridine and 3-hydroxyflavone compounds on a Ag nanocluster. One possible calculation method involves using the Gaussian package of programs for solutions to the coupled perturbed Hartree-Fock equations ( CPHF) for multiconfigurational CASSCF wave functions in order to obtain the frequency-dependent polarizability components. The Raman scattering intensities are then found from the differential scattering cross section by evaluating numerical derivatives of the dynamic polarizability as a function of Cartesian displacements of all atoms with respect to the equilibrium geometry. Other approaches to this calculation will be investigated in the ADF or MOLPRO packages for quantum chemistry.