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Date Permissions Signed

3-5-2021

Date of Award

Winter 2021

Document Type

Masters Thesis

Department or Program Affiliation

Chemistry

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Kowalczyk, Tim

Second Advisor

McCarty, Jay

Third Advisor

Rahmani, Armin

Abstract

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.

Type

Text

Keywords

DFTB, ROKS, Excited-State, semi-empirical, DFT

Publisher

Western Washington University

OCLC Number

1241705025

Subject – LCSH

Solar energy; Excited state chemistry; Density functionals; Electronic structures

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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