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Alternative title

Development of TI-DFTB

Date Permissions Signed

11-30-2020

Date of Award

Fall 2020

Document Type

Masters Thesis

Department or Program Affiliation

Chemistry

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Kowalczyk, Tim

Second Advisor

Berger, Robert F.

Third Advisor

Raymond, Elizabeth A.

Abstract

Here we discuss the development of a time-independent excited state computational method that consists of three augmentations to the semi-empirical electronic structure package, DFTB+ 19.1. The density functional based tight binding method (DFTB) is an approximation of Kohn-Sham (KS) density functional theory (DFT) wherein the energy functional is expanded to second order with respect to density fluctuations. Application of a delta self-consistent field (delta-SCF) approach within DFTB has allowed for the variationally optimized calculation of spin-purified excited state (ES) properties, and forms the foundation of our time-independent DFTB (TI-DFTB) framework. Selection of KS spin orbitals based on the character of the ES, and subsequent relaxation of these orbitals under non-Aufbau occupation constraints for both the singlet and triplet configuration is followed by application of the Ziegler sum rule to determine the time-independent spin purified ES of the system, its energy, and its optimized geometry. The maximum overlap method is an algorithmic restructuring of the typical DFTB variational charge optimization pathway, allowing differential relaxation pathways for difficult to converge molecules. Three variations of this approach have been implemented in DFTB+ 19.1, and are compatible with the time-independent ES method. The ground and excited electronic states resulting from a TI-DFTB calculation are made mutually orthogonal by a corresponding orbital transformation, thereby allowing calculation of transition properties like the transition dipole moment (TDM). Together these methods form a robust computational platform to investigate ES and transition information about chemical systems at low computational cost.

Type

Text

Keywords

DFTB, method development, computational chemistry, transition dipole moment

Publisher

Western Washington University

OCLC Number

1225205942

Subject – LCSH

Dipole moments; Computational chemistry; Excited state chemistry; Valence (Theoretical chemistry); Density functionals

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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