The eXact integral simplified time-dependent density functional theory (XsTD-DFT).

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Simplified time-dependent density functional theory (sTD-DFT) offers computational efficiency but requires approximations for integrals.
• Accurate prediction of excited states and nonlinear optical properties is crucial for materials science and drug discovery.

Purpose of the Study:

• Introduce and validate the eXact integral simplified time-dependent density functional theory (XsTD-DFT) method.
• Benchmark XsTD-DFT against established methods for excited-state and nonlinear response properties.
• Assess the computational efficiency and scalability of XsTD-DFT for large molecular systems.

Main Methods:

• Developed XsTD-DFT by replacing semi-empirical integrals in sTD-DFT with exact one- and two-center integrals.
• Evaluated performance on UV/Vis absorption, first hyperpolarizability, and two-photon absorption (2PA) for 77 molecules.
• Compared XsTD-DFT results with Time-Dependent Density Functional Theory (TD-DFT) and sTD-DFT data.

Main Results:

• XsTD-DFT/B3LYP excitation energies show minimal deviation (0.14 eV) from TD-DFT, with computational cost reduced by over 20 times.
• Accuracy for excitation energies increases with system size, demonstrating suitability for large molecules.
• XsTD-DFT improves upon sTD-DFT for excitation energies and oscillator strengths, especially for charge transfer states, and accurately reproduces hyperpolarizability and 2PA spectra.

Conclusions:

• XsTD-DFT provides TD-DFT accuracy at a fraction of the computational cost.
• The parameter-free nature and efficiency make XsTD-DFT ideal for large systems and high-throughput screening.
• This method opens new avenues for studying complex molecular systems and designing novel materials.