Natural Charge-Transfer Analysis: Eliminating Spurious Charge-Transfer States in Time-Dependent Density Functional Theory via Diabatization, with Application to Projection-Based Embedding

For many types of vertical excitation energies, linear-response time-dependent density functional theory (LR-TDDFT) offers a useful degree accuracy combined with unrivaled computational efficiency, although charge-transfer energies are often systematically and dramatically underestimated, especially for large systems those that contain explicit solvent. As result, low-energy electronic spectra solution-phase chromophores tens to hundreds spurious states, making LR-TDDFT needlessly expensive in bulk solution. Intensity borrowing by these states can affect intensities the valence excitations, altering bandshapes. At higher it is difficult distinguish from genuine charge-transfer-to-solvent (CTTS) excitations. In this work, we introduce an automated diabatization enables fast effective screening CTTS acceptor space Our procedure introduces “natural orbitals” provide means isolate orbitals most likely participate excitation. Projection onto solvent-centered virtual provides criterion defining important solvent molecules given be used as subspace selection algorithm projection-based embedding high-level description state lower-level its environment. We apply method ab initio molecular dynamics trajectory I–(aq) report lowest-energy band absorption spectrum. results excellent agreement experiment, only one-third water I–(H2O)96 simulation cell need described obtain converged <0.1 eV. The tools introduced herein will improve accuracy, usability environments.