A Study of Applicability of Density Functional Tight Binding—Molecular Mechanics Approach for the Calculation of Optical Properties

ABSTRACT Density functional tight binding (DFTB) and time‐dependent (TD)‐DFTB allow studying optical and electronic properties of materials at scales beyond the reach of Kohn–Sham density functional theory (DFT). Recently, DFTB‐MM was introduced in which some atomic pairs are treated via Slater–Koster (SK) parameterizations and some via molecular mechanics, extending applicability of DFTB to cases without accurate parameters for some atomic pairs. Here, we explore the applicability of DFTB‐MM to the calculation of optical properties with linear response TD‐DFTB. We use a molecule‐TiO 2 nanoparticle model system that exhibits an interfacial charge transfer band and modification of optical properties due to molecule‐nanoparticle orbital hybridization, as a stringent test for TD‐DFTB, which we compare to DFT with different functionals. We find that SK parameters for non‐bonded atomic pairs can be omitted with minimal effect on the quality of the spectrum and conclude that TD‐DFTB‐MM is viable for larger‐scale electronic structure and optical properties calculations.