Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China.
J Chem Phys. 2012 Sep 14;137(10):104311. doi: 10.1063/1.4749248.
A new four-dimensional ab initio potential energy surface for N(2)O-He is constructed at the CCSD(T) level with an aug-cc-pVQZ basis set together with bond functions. The vibrational coordinates Q(1) and Q(3) of N(2)O are explicitly included, due to the strong coupling between the symmetric and asymmetric stretches of N(2)O. A global potential energy surface is obtained by fitting the original potential points to a four-dimensional Morse∕long range (MLR) analytical form. In the fitting, the ab initio noise in the long range region of the potential is smoothed over by theoretically fixed long range parameters. Two-dimensional intermolecular potentials for both the ground and the excited υ(3) states of N(2)O are then constructed by vibrationally averaging the four-dimensional potential. Based on the two-dimensional potentials, we use the path integral Monte Carlo algorithm to calculate the vibrational band origin shifts for the N(2)O-He(N) clusters using a first order perturbation theory estimate. The calculated shifts agree reasonably well with the experimental values and reproduce the evolution tendency from dimer to large clusters.
构建了一个新的 N(2)O-He 的四维从头算势能面，在 aug-cc-pVQZ 基组和键函数的基础上，采用 CCSD(T)水平。由于 N(2)O 的对称和不对称伸展之间的强耦合，明确包含了 N(2)O 的振动坐标 Q(1)和 Q(3)。通过将原始势能点拟合到四维 Morse∕长程（MLR）解析形式，获得全局势能面。在拟合中，通过理论上固定的长程参数来平滑势能长程区域中的从头算噪声。然后通过振动平均四维势能来构建 N(2)O 的基态和激发 υ(3)态的二维分子间势能。基于二维势能，我们使用路径积分蒙特卡罗算法，使用一阶微扰理论估算，计算 N(2)O-He(N)团簇的振动带起源位移。计算得到的位移与实验值相当吻合，并再现了从二聚体到大团簇的演化趋势。
