Polarizable continuum model with the fragment molecular orbital-based time-dependent density functional theory

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate modeling of solvent effects is crucial for understanding molecular properties.
• Fragment-based methods offer a computationally efficient approach for large systems.
• Time-dependent density functional theory (TDDFT) is widely used for excited-state calculations.

Purpose of the Study:

• To develop and validate a hybrid computational method combining PCM and fragment molecular orbital-based TDDFT.
• To assess the accuracy of many-body contributions to singlet-excited states in solution.
• To investigate solvent effects and conformer contributions on excitation energies.

Main Methods:

• Integration of the polarizable continuum model (PCM) with fragment molecular orbital-based time-dependent density functional theory (TDDFT).
• Implementation of various levels of many-body expansion for fragment calculations.
• Application of the long-range corrected BLYP/6-31G* level for model calculations on phenol and polypeptides.

Main Results:

• The developed method demonstrated high accuracy, with a maximum error of 0.006 eV compared to full system TDDFT/PCM for systems up to 192 atoms.
• Nearly linear scaling was observed for solvent shifts and conformer effects.
• Accurate prediction of the lowest singlet excitation energy for the photoactive yellow protein (PYP) in aqueous solution, showing good agreement with experimental values.

Conclusions:

• The combined PCM and fragment molecular orbital-TDDFT approach is a reliable and efficient method for calculating excitation energies in solution.
• The method provides insights into the contributions of individual residues and solvent effects on protein excitation energies.
• This work advances the computational study of solvated molecular systems, particularly large biomolecules.