Performance of the simplified TD-DFT family of methods for the description of nonlinear optical properties: a benchmarking study

Kimika Teorikoa Seminar

In this presentation, I will introduce the family of simplified time-dependent density functional theory (sTD-DFT) methods. The methods were initially designed to reduce the computational cost of root TD-DFT calculations while retaining the essential physics of electronic interactions, enabling the calculation of vertical excitation energies for large to ultra-large systems surrounded by soft-matter environments (up to ~5000 atoms in total) with notable efficiency. However, today I will focus on the application of these methods for describing response properties instead of excitation energies, specifically addressing linear and nonlinear optical properties such as polarizability (α) and first hyperpolarizability (β). Although sTD-DFT approaches have been successfully employed to compute α and β in various biological systems, a comprehensive benchmarking study of their performance remains lacking. This will be the primary focus of my presentation. I will first assess the capability of sTD-DFT methods to reproduce conventional TD-DFT results and, where possible, compare the accuracy of both TD-DFT and sTD-DFT with reference CCSD(T) data. This allows us to identify the principal sources of error associated with the quantum-physical approximations in sTD-DFT and to highlight potential areas for methodological improvement.