Environmental Effects with Frozen-Density Embedding in Real-Time Time-Dependent Density Functional Theory Using...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Frozen-density embedding (FDE) is a method for describing environmental effects on molecular electron dynamics.
• Previous work extended FDE to real-time time-dependent Kohn-Sham (RT-TDDFT) using plane waves.
• Localized basis set implementations of RT-TDDFT are crucial for many molecular systems.

Purpose of the Study:

• To extend the RT-TDDFT method using localized basis sets to incorporate the FDE scheme.
• To investigate the numerical stability and accuracy of the combined FDE-RT-TDDFT approach.
• To explore the application of this method to phenomena like high harmonic generation (HHG).

Main Methods:

• Implementation of the uncoupled FDE scheme within the Psi4NumPy framework for RT-TDDFT.
• Utilized an efficient predictor/corrector second-order midpoint Magnus propagator with exact diagonalization.
• Adapted FDE implementation from the PyEmbed module of the PyADF scripting framework.

Main Results:

• The FDE potential did not introduce numerical instabilities in the time propagation of the density matrix.
• Low-lying transition energies in the weak field limit agreed with reference FDE calculations.
• Stable results were obtained even under strong external fields, and computational cost scaled linearly with environment size.

Conclusions:

• The developed FDE-RT-TDDFT method provides a stable and accurate approach for simulating molecular systems with environmental effects.
• The method shows promise for studying nonlinear optical phenomena like HHG, as demonstrated by preliminary water molecule simulations.
• The computational efficiency can be improved by reducing the updating frequency of the embedding potential.