An MO−VB Approach for the Determination of Intermolecular Forces. Theory and Calculations on the He2, He−CH4, and He−H2O Systems
An MO−VB Approach for the Determination of Intermolecular Forces. Theory and Calculations on the He2, He−CH4, and He−H2O Systems
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确定 He2、He−CH4 和 He−H2O 系统分子间力的 MO−VB 方法。
DOI：
10.1021/jp020681f
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发表时间：
2002
影响因子：
2.9
通讯作者：
M. Raimondi
中科院分区：
文献类型：
--
作者：
G. Calderoni;F. Cargnoni;A. Famulari;M. Raimondi
我们提出了以前开发的分子间力评估策略的改进。该方法定义了一个变分VB（价键）波函数，由来自SCF-MI（分子相互作用自洽场）行列式的单激发和双激发组成。该方法的核心思想是确定最优虚拟轨道，通过迭代优化程序压缩所有单激发和双激发局域构型所跨越的虚拟空间。通过与考虑全虚拟空间的结果进行比较来测试该策略的性能，并将整个方法与更传统的量子化学方法进行比较。给出了He2、He−CH4和He−H2O三种弱相互作用配合物的实验计算。无论研究什么系统，我们都发现VB、MP4和CCSD(T)的结果总体上是一致的。VB井深估计值略大于MP4和CCSD(T)。
We present the improvement of a previously developed strategy for the evaluation of intermolecular forces. The approach defines a variational VB (valence bond) wave function, consisting of single and double excitations from the SCF-MI (self-consistent field for molecular interactions) determinant. The central idea of the method is the determination of optimal virtual orbitals, to contract the virtual space spanned by all singly and doubly excited localized configurations, by means of an iterative optimization procedure. The performance of the strategy is tested by comparison with results where the full virtual space is considered, and the entire approach is also compared with more conventional quantum chemical methods. Test calculations on three weakly interacting complexes, namely, He2, He−CH4, and He−H2O, are presented. Whatever the system studied, we found an overall agreement between VB, MP4, and CCSD(T) results. The VB well depths estimates are somewhat larger than MP4 and CCSD(T) ones.