Multilevel DFT Response Theory.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of molecular response properties is crucial for understanding chemical phenomena.
• Existing methods often struggle with complex environments and long-range interactions.
• Polarizable quantum embedding frameworks offer a promising avenue for improved accuracy.

Purpose of the Study:

• To develop a general computational protocol for evaluating molecular response properties in complex environments.
• To extend multilevel density functional theory (MLDFT) to response theory.
• To couple MLDFT with a fluctuating-charge (FQ) force field for efficient long-range interaction modeling.

Main Methods:

• Formulation of coupled-perturbed Kohn-Sham (CPKS) equations within the MLDFT framework.
• Integration of a polarizable molecular mechanics layer using the FQ force field.
• Application to calculate static and frequency-dependent polarizabilities and hyperpolarizabilities.

Main Results:

• The protocol accurately computes linear polarizabilities and first hyperpolarizabilities for PNA and HBA in solution.
• Physicochemical insights into solute-solvent interactions were obtained, disentangling electrostatics, polarization, and quantum confinement.
• Results show excellent agreement with experimental data.

Conclusions:

• The developed computational protocol is reliable and robust for response property calculations.
• This method provides a viable route for incorporating response properties into quantum embedding methods.
• The framework enhances understanding of molecular behavior in complex chemical environments.