期刊
JOURNAL OF CHEMICAL PHYSICS
卷 133, 期 9, 页码 -出版社
AMER INST PHYSICS
DOI: 10.1063/1.3476468
关键词
ab initio calculations; configuration interactions; librational states; organic compounds; SCF calculations; vibrational states
资金
- Deutsche Forschungsgemeinschaft (DFG) [SFB-569/TP-N1]
In this paper, we couple a numerical kinetic-energy operator approach to the direct-vibrational self-consistent field (VSCF)/vibrational configuration interaction (VCI) method for the calculation of vibrational anharmonic frequencies. By combining this with fast-VSCF, an efficient direct evaluation of the ab initio potential-energy surface (PES), we introduce a general formalism for the computation of vibrational bound states of molecular systems exhibiting large-amplitude motion such as methyl-group torsion. We validate our approach on an analytical two-dimensional model and apply it to the methanol molecule. We show that curvilinear coordinates lead to a significant improvement in the VSCF/VCI description of the torsional frequency in methanol, even for a simple two-mode coupling expansion of the PES. Moreover, we demonstrate that a curvilinear formulation of the fast-VSCF/VCI scheme improves its speed by a factor of two and its accuracy by a factor of 3. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3476468]
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