Yagi Kiyoshi, Hirao Kimihiko, Taketsugu Tetsuya, Schmidt Michael W, Gordon Mark S
Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan.
J Chem Phys. 2004 Jul 15;121(3):1383-9. doi: 10.1063/1.1764501.
For polyatomic molecules, n-mode coupling representations of the quartic force field (nMR-QFF) are presented, which include terms up to n normal coordinate couplings in a fourth-order polynomial potential energy function. The computational scheme to evaluate third-and fourth-order derivatives by finite differentiations of the energy is fully described. The code to generate the nMR-QFF has been implemented into GAMESS program package and interfaced with the vibrational self-consistent field (VSCF) and correlation corrected VSCF (cc-VSCF) methods. As a demonstration, fundamental frequencies have been calculated by the cc-VSCF method based on 2MR-QFF for formaldehyde, ethylene, methanol, propyne, and benzene. The applications show that 2MR-QFF is a highly accurate potential energy function, with errors of 1.0-1.9% relative to the experimental value in fundamental frequencies. This approach will help quantitative evaluations of vibrational energies of a general molecule with a reasonable computational cost.
对于多原子分子，本文提出了四次力场的n模式耦合表示（nMR-QFF），其中包括在四阶多项式势能函数中高达n个正常坐标耦合的项。文中详细描述了通过能量的有限差分来评估三阶和四阶导数的计算方案。生成nMR-QFF的代码已被实现到GAMESS程序包中，并与振动自洽场（VSCF）和相关校正的VSCF（cc-VSCF）方法相连接。作为示例，基于2MR-QFF，通过cc-VSCF方法计算了甲醛、乙烯、甲醇、丙炔和苯的基频。应用表明，2MR-QFF是一种高度精确的势能函数，相对于基频的实验值，误差为1.0-1.9%。这种方法将有助于以合理的计算成本对一般分子的振动能量进行定量评估。
