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Master of Science (MS)
The restricted open-shell Kohn-Sham (ROKS) approach for singlet excited states provides some advantages over the ∆-self-consistent-field (∆SCF) method, requiring only a single SCF procedure and avoiding the problem of variational collapse. While ROKS is a powerful tool for DFT, its application to density functional tight-binding (DFTB) could offer significant improvements in time complexity when compared to DFT, enabling excited-state simulations of extended molecular systems on longer timescales than ROKS. In this work we discuss the implementation of an RO-DFTB approach in the DFTB+ package, as well as its suitability for the study of organic dyes and photoactive compounds. For benchmarking, RO-DFTB is evaluated using vertical excitation energies and Stokes shifts, with reference values from ROKS, higher levels of theory, and experiment. Numerical gradients are also computed to evaluate the RO-DFTB analytical geometry optimization. We compare several different versions of the RO-DFTB implementation, and use ∆DFTB to assess whether RO-DFTB can offer improvements over the current excited-state options in DFTB.
DFTB, ROKS, Excited-State, semi-empirical, DFT
Western Washington University
Subject – LCSH
Solar energy; Excited state chemistry; Density functionals; Electronic structures
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Szabo, Reuben, "Extension of Restricted Open-Shell Kohn-Sham Methodology to a Density-Functional Tight-Binding Framework" (2021). WWU Graduate School Collection. 1012.