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

Area of Science:

• Quantum chemistry
• Computational chemistry
• Spectroscopy

Background:

• Accurate description of electronic excited states is crucial for understanding photophysical and photochemical processes.
• Traditional methods often struggle to capture both static and dynamic electron correlation in excited states.
• Real-space energy decomposition methods offer intuitive interpretations of chemical bonding and reactivity.

Purpose of the Study:

• To implement and validate the interacting quantum atom (IQA) energy decomposition scheme within the complete active space second-order perturbation theory (CASPT2) framework.
• To develop a computational tool for analyzing energy redistribution in excited-state processes.
• To provide a detailed, real-space interpretation of chemical transformations involving complex electronic structures.

Main Methods:

• Implementation of the IQA energy decomposition scheme.
• Utilizing complete active space second-order perturbation theory (CASPT2) for accurate electronic structure calculations.
• Application to various chemical systems including noble gas excimers, ozone reactions, and photodissociations.

Main Results:

• The IQA/CASPT2 method successfully provides a real-space interpretation of energy changes during excited-state processes.
• The approach accurately accounts for static and dynamic electron correlation, essential for excited-state chemistry.
• Analysis of energy redistribution into self- and interatomic contributions offers detailed insights into reaction mechanisms.

Conclusions:

• The IQA/CASPT2 approach is a versatile tool for studying chemical processes with significant multiconfigurational character.
• This method enhances the understanding of energy flow in photophysical and photochemical deactivation pathways.
• The combination of IQA and CASPT2 provides valuable insights into bonding and reactivity across diverse chemical systems.