Analytic Gradient for Time-Dependent Density Functional Theory Combined with the Fragment Molecular Orbital Method.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of molecular properties requires efficient computational methods.
• Fragment Molecular Orbital (FMO) methods reduce computational cost for large systems.
• Time-Dependent Density Functional Theory (TDDFT) is crucial for studying excited electronic states.

Purpose of the Study:

• To derive and validate an analytic energy gradient for the FMO-TDDFT method.
• To incorporate polarizable embedding effects into the FMO-TDDFT gradient calculation.
• To enable accurate simulations of molecular dynamics and spectroscopy for excited states.

Main Methods:

• Derivation of the analytic energy gradient for FMO-TDDFT.
• Inclusion of response terms for polarizable embedding.
• Comparison with numerical FMO-TDDFT and unfragmented TDDFT gradients.
• Application to geometry optimization and excited-state simulations.

Main Results:

• The analytic FMO-TDDFT gradient was accurately derived.
• The gradient showed high accuracy compared to numerical and unfragmented methods.
• The method was successfully applied to optimize ground and excited states of a photoactive protein.

Conclusions:

• The developed analytic FMO-TDDFT gradient is a reliable tool for computational chemistry.
• This method enhances the accuracy of simulations for molecular geometry, dynamics, and spectra.
• It provides a robust approach for studying excited-state properties of large molecular systems.