Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand.
J Chem Phys. 2010 May 7;132(17):174304. doi: 10.1063/1.3408192.
We have calculated XH-stretching (where X=O, C, F, Cl) fundamental and overtone transitions for three diatomics and a few small molecules using a local mode model. The potential energy curves and dipole moment functions are calculated using the recently developed explicitly correlated coupled cluster with single doubles and perturbative triples theory [CCSD(T)-F12] with the associated VXZ-F12 (where X=D, T, Q) basis sets. We find that the basis set convergence of calculated frequencies and oscillator strengths obtained with the explicitly correlated method is much more rapid than with conventional CCSD(T) and the Dunning type correlation consistent basis sets. Furthermore, CCSD(T)-F12 frequencies and oscillator strengths obtained with the VTZ-F12 and VQZ-F12 basis sets are found to be in excellent agreement with the CCSD(T) complete basis set limit. We find that comparison of CCSD(T)-F12 frequencies with experiment is less good. The inclusion of explicit correlation exposes the inherent error of the CCSD(T) method to overestimate vibrational frequencies, which is normally compensated by basis set incompleteness error. As a consequence, we suggest that conventional CCSD(T) in combination with the aug-cc-pVTZ or aug-cc-pVQZ basis sets is likely to yield calculated XH-stretching frequencies in closest agreement with experiment.
我们使用局部模式模型计算了三个双原子和一些小分子的 XH 伸缩（其中 X=O、C、F、Cl）基频和泛频跃迁。使用最近开发的显式关联耦合簇加上单双和微扰三理论 [CCSD(T)-F12] 以及相关的 VXZ-F12（其中 X=D、T、Q）基组计算了势能曲线和偶极矩函数。我们发现，用显式相关方法计算的频率和振子强度的基组收敛速度比传统的 CCSD(T)和 Dunning 型相关一致基组快得多。此外，用 VTZ-F12 和 VQZ-F12 基组计算的 CCSD(T)-F12 频率和振子强度与 CCSD(T)完全基组极限非常吻合。我们发现，与实验相比，CCSD(T)-F12 频率的比较不太好。显式相关的包含暴露了 CCSD(T)方法高估振动频率的固有误差，通常由基组不完备误差补偿。因此，我们建议将传统的 CCSD(T)与 aug-cc-pVTZ 或 aug-cc-pVQZ 基组结合使用，可能会产生与实验最吻合的计算 XH 伸缩频率。
