Analytic gradients for state-averaged multiconfiguration pair-density functional theory | JoVE Visualize

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.