The accurate computation of partition functions in non-rigid molecules

被引:6
作者
Nino, A
MunozCaro, C
机构
[1] E.U. Info. de Ciudad Real, Universidad de Castilla-La Mancha, 13071 Ciudad Real
来源
COMPUTERS & CHEMISTRY | 1997年 / 21卷 / 03期
关键词
partition function; non-rigid molecules; HF dimer; equilibrium properties; ab initio calculations;
D O I
10.1016/S0097-8485(96)00032-0
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
A software tool for the computation of equilibrium properties in flexible, non-rigid, molecular systems is developed. The program can use semi-rigid and anharmonic models to obtain the rotational and vibrational contributions to the partition function. In addition, a semi-empirical procedure is developed to refine the partition function using experimental information. The program is employed to determine the quantitative performance of the semi-classical closed form for the computation of the rotational partition function. At standard temperature and for medium-size molecules, the error of the usual semi-classical form is found to be smaller than 0.1%. The refinement procedure is tested using the available values for the partition function of the (HF)(2) hydrogen-bonded complex. The partition function is computed using ab initio data obtained at the MP2(Full)/6-311 + + G(2df,2pd) level. Three models are tested: a pure harmonic model and two anharmonic models. In the anharmonic models, the potential for the hydrogen-bond stretching is described by a Taylor series or by a Morse function. The refinement technique is able to reproduce exactly the reference data in the three cases. (C) 1997 Elsevier Science Ltd.
引用
收藏
页码:143 / 151
页数:9
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