非迭代冻结密度近似方法在计算氢键相互作用的合理性研究

The study on hydrogen bonded systems using frozen density approximation

为计算相互作用较弱的分子碎片之间的耦合能 ,Harris从密度泛函理论出发 ,提出了一种简化方法 ,即冻结密度近似 (FDA)方法 .对该方法在描述分子间氢键作用的合理性进行了验证 .对水分子间的HO┉H氢键、甲酰胺与水分子间的 NH┉O 氢键、二氟甲烷和水分子间的 OH┉F 氢键 ,以及DNA中的碱基 (AT ,GC )之间的N—H┉O ,N—H┉N等类型的氢键的计算表明 :若电子交换关联采用非定域自旋密度近似 ,FDA的计算结果同其他abinitio方法的计算结果以及实验结果都符合得很好 .FDA在计算过程中既不需要求解泊松方程 ,也不需要进行反复的自洽迭代 ,所以运算速度较快 。

A method, so called frozen density approximation (FEA), for calculating approximately the coupling energy of weakly interacting fragments was developed by Harris. The method is a simplified version of the density functional theory (DFT) of Kohn and Sham. In the present work, we use this method to study hydrogen bonded systems. As a test of the applicability of FDA to the systems containing hydrogen bonds, linear combination of Gaussian type orbitals calculations within the generalized gradient approximation (GGA) have been performed on five intermolecular hydrogen bonded systems, such as water dimer, formamide water complex, difluoromethane water complex, and Waston Crick base pairs (G—C, and A—T). The results show that the hydrogen bond energies and the equilibrium structural parameters obtained by using FDA are in good agreement with those given by using other ab initio methods as well as experiments, when the GGA of electron exchange correlation was employed. Neither self consistency cycling nor a solution of Poisson's equation for the systems is required. The running time is therefore greatly saved, while the accuracy of this method is also comparable to that of DFT calculation. This simplified method has a potential applicability on the relatively large systems of biological importance containing hydrogen bonds, such as nucleic acid and protein.