精确计算(NH_3)_2缔合体结构和稳定性的方案研究(英文)

Studies on Accurate Quantum-chemical Calculation of the Geometries and Stabilities of(NH_3)_2 Cluster

采用不同方法、在不同基组水平上系统地对(NH3)2缔合体进行构型优化和结合能计算,并和实验值做详细比较。(1)对于弱氢键体系(NH3)2,B3LYP和HF计算结果不可靠;(2)适合(NH3)2体系的最好计算方案是MP2/6-311++G**(如果基组不低于6-31++G**水平,计算结果也可取),但是必须做BSSE校正。(3)基组中不加弥散函数只能得到一种环状构型,加入弥散函数可以得到两种构型。(4)对于弱相互作用体系,在选用计算方法和基组前应该做充分的方法验证。

Geometry optimization and calculation of binding energy of the system of （NH3）2 were carried out by different methods at different levels of basis set systematically, and all the computational structural parameters were compared with the experimental ones. Both B3LYP and HF are not suitable for the weak hydrogen bond system of （NH3）2. The best method is MP2/6-31 1＋＋G＊＊, and the BSSE must be corrected. Diffuse function plays an important role in the geometry optimization, i.e., there are two geometries of ring and line augmented with a diffuse function and only one geometry of ring otherwise. The binding energy of the ringy geometry is lower than that of the linear geometry. It is constructive that an elaborate comparison is necessary to make before any method or basis set is adopted for a weak interactional system.