Using monomer vibrational wavefunctions to compute numerically exact (12D) rovibrational levels of water dimer.
Using monomer vibrational wavefunctions to compute numerically exact (12D) rovibrational levels of water dimer.
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DOI：
10.1063/1.5020426
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发表时间：
2018-02
期刊：
影响因子：
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通讯作者：
Xiao-Gang Wang;T. Carrington
中科院分区：
文献类型：
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作者：
Xiao-Gang Wang;T. Carrington
我们在精确的CCpol-8sf从头算柔性单体势能面上计算了具有12个振动坐标的水二聚体的精确振动能级[C.LeForestier等人，J.化学]。太棒了。137、014305(2012年)]。它没有乘积和或多模形式，因此必须使用某种形式的求积。为了进行计算，有必要使用有效的基组，并开发计算工具，以评估计算频谱所需的矩阵-矢量乘积，从而消除将势存储在12维正交网格上的需要。我们使用的基函数是单体振动波函数和标准刚性单体基函数(涉及三个Wigner函数的乘积)的乘积。势能矩阵-矢量乘积使用F矩阵思想来评估，以前用来计算5原子和6原子分子的转动能级。当单体间和单体内坐标之间的耦合很弱时，这种粗绝热基是有效的(只需要几个单体振动波函数)，尽管矩阵元素的计算很简单。它比绝热基础上使用起来容易得多。基函数的乘积结构与动能算符的乘积结构相容，便于矩阵向量积的计算。与用[6+6]D绝热方法得到的结果相比，我们发现分子间的能级符合得很好，而分子内水弯曲能级的差异较大。
We compute numerically exact rovibrational levels of water dimer, with 12 vibrational coordinates, on the accurate CCpol-8sf ab initio flexible monomer potential energy surface [C. Leforestier et al., J. Chem. Phys. 137, 014305 (2012)]. It does not have a sum-of-products or multimode form and therefore quadrature in some form must be used. To do the calculation, it is necessary to use an efficient basis set and to develop computational tools, for evaluating the matrix-vector products required to calculate the spectrum, that obviate the need to store the potential on a 12D quadrature grid. The basis functions we use are products of monomer vibrational wavefunctions and standard rigid-monomer basis functions (which involve products of three Wigner functions). Potential matrix-vector products are evaluated using the F matrix idea previously used to compute rovibrational levels of 5-atom and 6-atom molecules. When the coupling between inter- and intra-monomer coordinates is weak, this crude adiabatic type basis is efficient (only a few monomer vibrational wavefunctions are necessary), although the calculation of matrix elements is straightforward. It is much easier to use than an adiabatic basis. The product structure of the basis is compatible with the product structure of the kinetic energy operator and this facilitates computation of matrix-vector products. Compared with the results obtained using a [6 + 6]D adiabatic approach, we find good agreement for the inter-molecular levels and larger differences for the intra-molecular water bend levels.