Department of Chemistry & Biochemistry, University of Mississippi, University, Mississippi 38677-1848, United States.
J Phys Chem A. 2023 Jun 8;127(22):4771-4779. doi: 10.1021/acs.jpca.3c00072. Epub 2023 May 26.
Quartic force fields (QFFs) constructed using a sum of ground-state CCSD(T)-F12b energies with EOM-CCSD excitation energies are proposed for computation of spectroscopic properties of electronically excited states. This is dubbed the F12+EOM approach and is shown to provide similar accuracy to previous methodologies at lower computational cost. Using explicitly correlated F12 approaches instead of canonical CCSD(T), as in the corresponding (T)+EOM approach, allows for 70-fold improvement in computational time. The mean percent difference between the two methods for anharmonic vibrational frequencies is only 0.10%. A similar approach is also developed herein which accounts for core correlation and scalar relativistic effects, named F12cCR+EOM. The F12+EOM and F12cCR+EOM approaches both match to within 2.5% mean absolute error of experimental fundamental frequencies. These new methods should help in clarifying astronomical spectra by assigning features to vibronic and vibrational transitions of small astromolecules when such data are not available experimentally.
提出了一种使用基态 CCSD(T)-F12b 能量求和加上 EOM-CCSD 激发能构建的四次力场 (QFF) ，用于计算电子激发态的光谱性质。这被称为 F12+EOM 方法，与先前的方法相比，它在更低的计算成本下提供了相似的准确性。与相应的 (T)+EOM 方法中使用规范 CCSD(T) 不同，使用显式相关的 F12 方法，如在 F12 方法中，可以将计算时间提高 70 倍。两种方法之间的非谐振动频率的平均百分比差异仅为 0.10%。本文还开发了一种类似的方法，该方法考虑了核心相关和标量相对论效应，称为 F12cCR+EOM。F12+EOM 和 F12cCR+EOM 两种方法都与实验基本频率的平均绝对误差在 2.5%以内相匹配。当实验上无法获得此类数据时，这些新方法应该有助于通过将特征分配给小型天体分子的振动态和振动跃迁来澄清天体光谱。
