Time-Dependent Complete Active Space Embedded in a Polarizable Force Field.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Spectroscopy

Background:

• Electron correlation and environmental effects significantly influence chemical system dynamics.
• Understanding these effects is crucial for interpreting spectroscopic data in condensed phases.

Purpose of the Study:

• To present a novel time-dependent complete active space configuration interaction (TD-CASCI) method integrated with a polarizable force field (MMPol).
• To enable the study of large chemical systems by employing a direct matrix-vector contraction scheme.
• To investigate the solvatochromic shift of coumarin 153 in methanol using the developed TD-CASCI/MMPol approach.

Main Methods:

• Implementation of a direct matrix-vector contraction for TD-CASCI/MMPol.
• Application to study the solvatochromic shift of coumarin 153 in methanol.
• Comparison with linear response time-dependent density functional theory (LR-TDDFT).

Main Results:

• The TD-CASCI/MMPol approach accurately captures double excitation character in excited states.
• It precisely predicts the experimental solvatochromic red-shift for coumarin 153 in methanol.
• The method demonstrates superior performance compared to LR-TDDFT for this system.

Conclusions:

• The TD-CASCI/MMPol method provides an accurate and efficient tool for studying electron dynamics and spectroscopic properties in condensed phases.
• The study highlights the importance of an unbiased treatment of electronic states for accurate simulations.
• This approach advances the understanding of solvation effects on molecular properties.