Implementation of the interacting quantum atom energy decomposition using the CASPT2 method

• Published in: Physical chemistry chemical physics : PCCP Vol. 23; no. 48; pp. 2758 - 27519
• Main Authors: Jara-Cortés, Jesús, Leal-Sánchez, Edith, Francisco, Evelio, Pérez-Pimienta, José A, Martín Pendás, Ángel, Hernández-Trujillo, Jesús
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 15.12.2021
• Subjects: Chemical reactions; Chlorine; Cyclobutane; Decomposition; Excimers; Perturbation theory; Rare gases
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d1cp02837e

We present an implementation of the interacting quantum atom (IQA) energy decomposition scheme using the complete active space second-order perturbation theory (CASPT2). This combination yields a real-space interpretation tool with a proper account of the static and dynamic correlation that is particularly relevant for the description of processes in electronic excited states. The IQA/CASPT2 approach allows determination of the energy redistribution that takes place along a photophysical/photochemical deactivation path in terms of self- and interatomic contributions. The applicability of the method is illustrated by the description of representative processes spanning different bonding regimes: noble gas excimer and exciplex formation, the reaction of ozone with a chlorine atom, and the photodissociations of formaldehyde and cyclobutane. These examples show the versatility of using CASPT2 with the significant information provided by the IQA partition to describe chemical processes with a large multiconfigurational character. The IQA energy decomposition analysis at the CASPT2 level of theory allows to obtain chemical insight about multiconfigurational processes.