Analytic gradients for state-averaged multiconfiguration pair-density functional theory

Area of Science:

• Quantum Chemistry
• Computational Spectroscopy
• Theoretical Photochemistry

Background:

• Analytic gradients are crucial for accurately calculating molecular properties and dynamics.
• State-averaged complete active space self-consistent-field (SA-CASSCF) provides a foundation for excited-state calculations but often requires costly post-processing for quantitative accuracy.
• Existing post-SA-CASSCF methods like perturbation theory and configuration interaction can be computationally prohibitive.

Purpose of the Study:

• To present and validate analytic gradients for multiconfiguration pair-density functional theory (MCPDFT) built upon SA-CASSCF wave functions.
• To provide a more computationally affordable approach for accurate excited-state geometry optimizations and energy calculations.
• To assess the accuracy of MCPDFT analytic gradients by comparing results with established literature methods.

Main Methods:

• Development of analytic gradient expressions for MCPDFT calculations.
• Utilizing SA-CASSCF as the reference wave function for MCPDFT.
• Application to a test set of molecules to compute stationary geometries and energetics.
• Comparison of MCPDFT results with literature data obtained from other quantum chemical methods.

Main Results:

• Successful implementation and demonstration of analytic gradients for SA-CASSCF-based MCPDFT.
• MCPDFT calculations provide accurate excited-state geometries and energetics.
• The computational cost of MCPDFT is significantly lower than traditional post-SA-CASSCF methods.
• Excited-state geometries obtained via state-averaged pair-density functional theory show comparable accuracy to second-order complete active space perturbation theory.

Conclusions:

• Analytic gradients for SA-CASSCF-based MCPDFT represent a significant advancement in computational chemistry.
• This method offers a practical and accurate alternative for studying excited-state phenomena.
• The findings pave the way for more routine and cost-effective investigations in UV-Vis spectroscopy and photochemistry.