A new framework for frequency-dependent polarizable force fields.

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Quantum Mechanics

Background:

• The Atom-Condensed Kohn-Sham density functional theory approximated to the second-order (ACKS2) is a polarizable force field.
• Predicting dynamical response properties of finite systems requires frequency-dependent molecular response functions.

Purpose of the Study:

• To propose a frequency-dependent extension of the ACKS2 force field, named ACKS2ω.
• To enable theoretical predictions of dynamical response properties for finite systems.

Main Methods:

• The ACKS2ω method extends the ACKS2 force field to include frequency dependence.
• Parameters are computed as expectation values of electronic wavefunctions, reusing the ACKS2 hardness matrix via an adiabatic approximation.
• Numerical validation uses atomic monopoles and dipoles.

Main Results:

• Absorption spectra of 42 molecular monomers calculated with ACKS2ω show good agreement with time-dependent DFT (TDDFT).
• C6 dispersion coefficients calculated by ACKS2ω closely reproduce TDDFT references.
• For 903 intermolecular pairs, ACKS2ω parameters derived from PBE/aug-cc-pVDZ yield an MAPE of 3.84% compared to experimental values.

Conclusions:

• The ACKS2ω method provides accurate predictions of dynamical response properties.
• It establishes a strong link between quantum mechanical descriptions and efficient force field models.
• The method is validated for molecular spectra, dispersion coefficients, and intermolecular interactions.