Analytic First-Order Derivatives of CASPT2 Combined with the Polarizable Continuum Model

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Complete active space second-order perturbation theory (CASPT2) is crucial for accurate electronic structure and transition energy predictions.
• Optimizing molecular geometries in solution phase using CASPT2 presents significant computational challenges.

Purpose of the Study:

• To develop analytic first-order derivatives for CASPT2 calculations incorporating implicit solvation.
• To enable accurate molecular geometry optimization in solution phase using CASPT2.

Main Methods:

• Implementation of analytic first-order derivatives of CASPT2 with the polarizable continuum model (PCM) for implicit solvation.
• Utilizing the open-source computational chemistry package OpenMolcas.
• Solving a modified Z-vector equation to compute analytic gradients and nonadiabatic coupling vectors.

Main Results:

• Successfully developed and implemented analytic gradients for CASPT2 with implicit solvation.
• Demonstrated the capability to qualitatively capture solvent effects on molecular properties.
• Validated the method through comparisons with existing theoretical and experimental data.

Conclusions:

• The developed method provides a robust approach for geometry optimization of molecules in solution.
• This advancement enhances the accuracy and applicability of CASPT2 calculations in condensed-phase environments.
• The study paves the way for more reliable computational studies of chemical systems in solution.