Budzák Šimon, Scalmani Giovanni, Jacquemin Denis
Department of Chemistry, Faculty of Natural Sciences, Matej Bel University , Tajovského 40, SK-97400 Banská Bystrica, Slovak Republic.
Gaussian Incorporated , 340 Quinnipiac Street, Building 40, Wallingford, Connecticut 06492 United States.
J Chem Theory Comput. 2017 Dec 12;13(12):6237-6252. doi: 10.1021/acs.jctc.7b00921. Epub 2017 Dec 1.
We present an investigation of the excited-state structural parameters determined for a large set of small compounds with the dual goals of defining reference values for further works and assessing the quality of the geometries obtained with relatively cheap computational approaches. In the first stage, we compare the excited-state geometries obtained with ADC(2), CC2, CCSD, CCSDR(3), CC3, and CASPT2 and large atomic basis sets. It is found that CASPT2 and CC3 results are generally in very good agreement with one another (typical differences of ca. 3 × 10 Å) when all electrons are correlated and when the aug-cc-pVTZ atomic basis set is employed with both methods. In a second stage, a statistical analysis reveals that, on the one hand, the excited-state (ES) bond lengths are much more sensitive to the selected level of theory than their ground-state (GS) counterparts and, on the other hand, that CCSDR(3) is probably the most cost-effective method delivering accurate structures. Indeed, CCSD tends to provide too compact multiple bond lengths on an almost systematic basis, whereas both CC2 and ADC(2) tend to exaggerate these bond distances, with more erratic error patterns, especially for the latter method. The deviations are particularly marked for the polarized CO and CN bonds, as well as for the puckering angle in formaldehyde homologues. In the last part of this contribution, we provide a series of CCSDR(3) GS and ES geometries of medium-sized molecules to be used as references in further investigations.
我们对大量小分子化合物的激发态结构参数进行了研究，目的有二：一是为后续研究确定参考值，二是评估用相对廉价的计算方法获得的几何结构的质量。在第一阶段，我们比较了用ADC(2)、CC2、CCSD、CC3、CC3和CASPT2以及大原子基组获得的激发态几何结构。结果发现，当所有电子都相关且两种方法都采用aug-cc-pVTZ原子基组时，CASPT2和CC3的结果通常非常吻合（典型差异约为3×10 Å）。在第二阶段，统计分析表明，一方面，激发态（ES）键长比基态（GS）键长对所选理论水平更为敏感，另一方面，CC3可能是提供精确结构的最具成本效益的方法。实际上，CCSD几乎系统性地倾向于给出过于紧凑的多重键长，而CC2和ADC(2)则倾向于夸大这些键距，且误差模式更不稳定，尤其是后者。对于极化的CO和CN键以及甲醛同系物中的褶皱角，偏差尤为明显。在本论文的最后部分，我们提供了一系列中等大小分子的CC3基态和激发态几何结构，以供后续研究作为参考。
