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Development of TI-DFTB
Date Permissions Signed
Date of Award
Department or Program Affiliation
Master of Science (MS)
Berger, Robert F.
Raymond, Elizabeth A.
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.
DFTB, method development, computational chemistry, transition dipole moment
Western Washington University
Subject – LCSH
Dipole moments; Computational chemistry; Excited state chemistry; Valence (Theoretical chemistry); Density functionals
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Deshaye, Megan, "Development of TI-DFTB: Transition Dipole Moment Calculations in a Time-Independent Density Functional Tight-Binding Framework" (2020). WWU Graduate School Collection. 990.