Ab initio floating occupation molecular orbital-complete active space configuration interaction: an efficient...

Area of Science:

• Quantum chemistry
• Computational chemistry
• Theoretical chemistry

Background:

• Accurate electronic structure calculations are crucial for understanding molecular behavior.
• Photochemistry and photodynamics require robust methods to describe excited states.
• Existing methods like SA-CASSCF can be computationally demanding.

Purpose of the Study:

• To implement and evaluate a novel ab initio method, FOMO-CASCI.
• To assess the suitability of FOMO-CASCI for photochemistry and photodynamics.
• To compare FOMO-CASCI with established methods like SA-CASSCF.

Main Methods:

• Implementation of a complete active space configuration interaction (CASCI) method.
• Utilizing floating occupation molecular orbitals (FOMOs) for improved active space definition.
• Ab initio electronic structure calculations.

Main Results:

• FOMO-CASCI provides a good approximation to SA-CASSCF.
• The FOMO-CASCI method demonstrates enhanced efficiency and stability compared to SA-CASSCF.
• Identified specific cases where FOMO-CASCI may present challenges.

Conclusions:

• FOMO-CASCI is a promising and efficient alternative for ab initio photodynamics.
• The method offers a balance of accuracy and computational feasibility.
• Further development and exploration of FOMO-CASCI extensions are warranted.