Mixed Planewave and Localized Orbital Basis for Sparse-Stochastic Hybrid Time-Dependent Density Functional Theory.

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• Accurate calculation of optical absorption spectra is crucial for understanding molecular electronic properties.
• Traditional methods using plane-wave basis sets can be computationally expensive, especially for large systems.
• Time-dependent density functional theory (TD-DFT) is a powerful tool for predicting spectra but requires efficient implementations.

Purpose of the Study:

• To develop a novel mixed basis-set approach for calculating optical absorption spectra.
• To improve the computational efficiency and accelerate spectral convergence in TD-DFT calculations.
• To enable efficient evaluation of the exact exchange operator within this new framework.

Main Methods:

• A generalized Kohn-Sham time-dependent density functional theory (TD-DFT) framework is employed.
• A mixed basis-set approach is utilized: occupied valence molecular orbitals (MOs) use a plane-wave (PW) basis, while unoccupied MOs use localized atomic basis functions.
• The method leverages a common real-space grid for efficient evaluation of the exact exchange operator.

Main Results:

• The mixed basis-set approach significantly accelerates spectral convergence compared to fully PW-based simulations.
• A 2-3 fold reduction in the number of unoccupied MOs required for the Casida equation is achieved.
• The method demonstrates computational efficiency and chemical intuition across diverse molecular systems.

Conclusions:

• The developed mixed basis-set approach offers a computationally efficient and accurate method for calculating optical absorption spectra.
• This method provides a significant speed-up in spectral convergence, making TD-DFT calculations more accessible.
• The approach is validated for various systems, including polymethine dyes, aromatic hydrocarbons, and chlorophyll.