Nonlinear-response properties in a simplified time-dependent density functional theory (sTD-DFT) framework:...

Area of Science:

• Quantum Chemistry
• Computational Spectroscopy
• Microscopy

Background:

• Nonlinear imaging microscopy requires efficient theoretical tools for characterizing nonlinear optical properties.
• Quantum chemistry can aid in designing new dyes and understanding biological systems for second-harmonic imaging microscopy (SHIM).
• Existing methods struggle with screening numerous compounds and analyzing large biological systems efficiently.

Purpose of the Study:

• To present a novel simplified time-dependent density functional theory (sTD-DFT) implementation for evaluating first hyperpolarizability.
• To develop an ultra-fast tight-binding version (sTD-DFT-xTB) for rapid hyperpolarizability calculations.
• To enable efficient screening of compounds and analysis of large systems for SHIM applications.

Main Methods:

• Developed a simplified time-dependent density functional theory (sTD-DFT) approach.
• Approximated Coulomb and exchange integrals using short-range damped Coulomb interactions of transition density monopoles.
• Introduced a tight-binding version (sTD-DFT-xTB) for further acceleration.

Main Results:

• The sTD-DFT implementation is over 600 times faster than regular TD-DFT.
• The sTD-DFT-xTB version offers an additional speed-up of at least two orders of magnitude.
• The method was successfully tested on push-pull π-conjugated compounds, fluorescent proteins, and a collagen model.

Conclusions:

• The new sTD-DFT and sTD-DFT-xTB methods provide efficient tools for calculating first hyperpolarizability.
• These methods can significantly accelerate the design of new dyes and the study of biological systems for SHIM.
• The computational efficiency allows for screening large numbers of compounds and analyzing complex biological structures.