Analytical Nuclear Gradients for the Multiconfigurational Self-Consistent Field Method Coupled with the Polarizable...

Area of Science:

• Computational chemistry
• Theoretical chemistry
• Molecular spectroscopy

Background:

• Accurate simulation of molecular properties requires sophisticated computational models.
• Understanding solute-solvent interactions is crucial for predicting spectra in solution.
• Existing models may struggle to capture both multireference electronic character and dynamic solvation effects.

Purpose of the Study:

• To extend the multiscale multiconfigurational self-consistent field (MCSCF) and Fluctuating Charges (FQ) model to compute analytical nuclear gradients.
• To implement and validate these gradients for simulating vibronic absorption spectra.
• To assess the model's ability to describe molecular flexibility and solvent dynamics.

Main Methods:

• First-principles derivation and implementation of MCSCF/FQ nuclear gradients in OpenMolcas.
• Validation against numerical references.
• Integration with molecular dynamics simulations for vibronic spectra calculation.

Main Results:

• Successful implementation of analytical nuclear gradients for the MCSCF/FQ model.
• Accurate simulation of vibronic absorption spectra for benzene and phenol in aqueous solution.
• Excellent agreement with experimental band profiles and intensities.

Conclusions:

• The extended MCSCF/FQ model accurately captures multireference character and solvent interactions.
• The approach effectively simulates vibronic spectra by including conformational and dynamical solvation effects.
• This method provides a powerful tool for studying complex molecular systems in solution.