Dielectric-Screened Functionals for Cis–Trans Excitation Energies of Solvated Azobenzene Derivatives: Screening Trends in Comparison with Experiment and Published GW/BSE Calculations

Abstract

Accurate modeling of electronically excited states in solution is essential for the rational design of photoactive molecular systems, but requires a reliable treatment of environmental effects. We present a mean-field approach that combines density functional theory with a polarizable continuum model (PCM) to account for environmental dielectric screening, providing an efficient mean-field alternative to higher-cost wavefunction- or many-body-based approaches. The framework employs dielectric-screened range-separated hybrid (SRSH) functionals within PCM to obtain excited states of solvated azobenzene derivatives, a prototypical molecular photoswitch. SRSH–PCM excitation energies better reproduce experiment when the larger static dielectric constant, which also accounts for nuclear polarization, is used to define long-range screening. Using the smaller optical dielectric constant, which represents purely electronic polarization, SRSH–PCM energies align better with previously reported high-quality GW–Bethe–Salpeter equation (GW/BSE) energies [Kshirsagar et al., JCTC 2020]. Our findings demonstrate that mean-field SRSH–PCM provides an effective description of excited-state properties while offering insights into the role of environmental screening and, in particular, the importance of accounting for nuclear contributions to dielectric screening in many-body calculations of solution-phase excitation energies.