Owens Alec
Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT, London, UK.
Phys Chem Chem Phys. 2024 Jun 26;26(25):17684-17694. doi: 10.1039/d4cp01205d.
quantum chemical methods can produce accurate molecular potential energy surfaces (PESs) capable of predicting the fundamental vibrational wavenumbers to within 1 cm. However, for high-resolution applications this is simply not good enough and empirical refinement is necessary, adjusting the PES to better match laboratory spectroscopic data. Here, the impact of the underlying calculations is rigorously investigated within the context of empirical refinement. For carbonyl sulphide (OCS), state-of-the-art electronic structure calculations are employed to construct higher- and lower-level PESs, which are then empirically refined in near-identical procedures. The initial calculations are shown to considerably affect the accuracy of the final refined PES, with an order-of-magnitude improvement in computed rotation-vibration energy levels achieved for OCS. In demonstrating this, the most accurate PES of the electronic ground state of OCS is produced, reproducing the fundamentals with a root-mean-square error (RMSE) of 0.004 cm, and 884 rovibrational energy levels below 14 000 cm with an RMSE of 0.060 cm.
量子化学方法能够生成精确的分子势能面（PESs），可以将基本振动波数预测到1厘米以内。然而，对于高分辨率应用而言，这还远远不够，必须进行经验性优化，调整势能面以更好地匹配实验室光谱数据。在此，在经验性优化的背景下，对基础计算的影响进行了严格研究。对于羰基硫（OCS），采用了最先进的电子结构计算来构建高低不同层级的势能面，然后通过几乎相同的程序进行经验性优化。结果表明，初始计算对最终优化后的势能面的准确性有很大影响，羰基硫的计算转动 - 振动能级实现了一个数量级的提升。通过这一过程，生成了羰基硫电子基态最精确的势能面，其基频的均方根误差（RMSE）为0.004厘米，在14000厘米以下的884个振转能级的RMSE为0.060厘米。
