NH_3(H_2O)_4稳定结构的理论研究

Stable Structures of Binary Molecular Cluster of NH_3(H_2O)_4

先构建氨水团簇的模型势,并计算得到NH3(H2O)4的模型势异构体,从中选取稳定性较好的异构体作为初始结构,分别利用密度泛函方法和二级微扰理论在6-31G(d)和6-311++G(d,p)基组水平上逐级进行结构优化、频率和单点能计算.发现包括第2和第3稳定结构等12种新异构体;NH3(H2O)4的五边形环状结构的稳定性最好;这种极性混合分子簇的偶极矩大小和包含的氢键数都与结构的稳定性无必然联系.

An empirical potential of binary molecular clusters of （ NH ） m （ H2O）n is proposed. Stable model structures of NH3 （H2O）4 are optimized by using a fast molecular dynamics algorithm. The optimal structures are refined by using conventional ab initio optimization method. Optimization and frequency calculations are carried out at different levels of density functional theory （DFT/ B3LYP） and Moller-Plesset second-order perturbation method （MP2） with 6-311 ＋ ＋G＊＊ basis set. It is found that stable model structures remain the minima at B3LYP and MP2 levels. 12 new ab initio stable isomers of NH3 （H2O）4 including the second and third ones are obtained. The results show that there is no inevitable relevancy between stability and dipole moment, and the number of hydrogen bonds of isomers.