Reference Vertical Excitation Energies for Transition Metal Compounds

TL;DR

This paper expands the extsc{quest} database by providing high-accuracy vertical excitation energies for eleven transition metal diatomic molecules using advanced coupled-cluster and multiconfigurational methods, and compares these with experimental data.

Contribution

It introduces benchmark transition energies for transition metal compounds computed with high-level methods, enriching the existing database and enabling method performance assessment.

Findings

High-level coupled-cluster and multiconfigurational methods yield consistent excitation energies.

Benchmark data in aug-cc-pVDZ and aug-cc-pVTZ basis sets established.

Comparisons with experimental data validate the computational approaches.

Abstract

To enrich and enhance the diversity of the \textsc{quest} database of highly-accurate excitation energies [\href{https://doi.org/10.1002/wcms.1517}{V\'eril \textit{et al.}, \textit{WIREs Comput.~Mol.~Sci.}~\textbf{11}, e1517 (2021)}], we report vertical transition energies in transition metal compounds. Eleven diatomic molecules with singlet or doublet ground state containing a fourth-row transition metal (\ce{CuCl}, \ce{CuF}, \ce{CuH}, \ce{ScF}, \ce{ScH}, \ce{ScO}, \ce{ScS}, \ce{TiN}, \ce{ZnH}, \ce{ZnO}, and \ce{ZnS}) are considered and the corresponding excitation energies are computed using high-level coupled-cluster (CC) methods, namely CC3, CCSDT, CC4, and CCSDTQ, as well as multiconfigurational methods such as CASPT2 and NEVPT2. In some cases, to provide more comprehensive benchmark data, we also provide full configuration interaction estimates computed with the \textit{"Configuration Interaction using a Perturbative Selection made Iteratively"} (CIPSI) method. Based on these calculations, theoretical best estimates of the transition energies are established in both the aug-cc-pVDZ and aug-cc-pVTZ basis sets. This allows us to accurately assess the performance of CC and multiconfigurational methods for this specific set of challenging transitions. Furthermore, comparisons with experimental data and previous theoretical results are also reported.