Event Title

Calculation of excited state characteristics and electronic transition dipole moments in time-independent DFTB

Research Mentor(s)

Tim Kowalczyk

Description

The density functional based tight binding method (DFTB) is an approximation of Kohn-Sham (KS) DFT wherein the exchange correlation energy functional is expanded to the second order with respect to charge density fluctuations. Augmentation of this method as implemented in DFTB+ has allowed for the variationally optimized calculation of spin-purified excited state properties with application in spectral prediction and efficient description of large excited systems. Selection of KS spin orbitals based on the character of the excited state, 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 result in the spin purified virtual state of the system revealing its energy and optimized geometry. The ability to describe properties of an excited system along a molecular dynamics trajectory allows for simulation of spectroscopies used to describe photophysical relaxation. The electronic transition dipole moment (TDM) is a useful property to describe as it dictates the intensity of electronic transition, corresponding to the intensity of spectral peaks. The TDM is also useful in deriving rates of energy transfer in excited donor-acceptor systems. Calculation of TDMs within a DFTB framework is complicated by the fact that ground and excited states though separately orthogonal are not mutually so, therefore a corresponding orbital transformation must be applied to the molecular orbitals of the ground and excited-state to ensure orthogonality. Benchmarking of this work will be directly compared to similar calculations in EOM-CCSD and TD-DFT, both methods noted for their level of accuracy that scales with their computational expense. Successful porting of these calculations into DFTB+ creates an accessible method for high throughput screening of large photoactive systems with application in alternative energy solutions.

Document Type

Event

Start Date

15-5-2019 9:00 AM

End Date

15-5-2019 5:00 PM

Location

Carver Gym (Bellingham, Wash.)

Department

Chemistry

Genre/Form

student projects, posters

Type

Image

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.

Language

English

Format

application/pdf

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May 15th, 9:00 AM May 15th, 5:00 PM

Calculation of excited state characteristics and electronic transition dipole moments in time-independent DFTB

Carver Gym (Bellingham, Wash.)

The density functional based tight binding method (DFTB) is an approximation of Kohn-Sham (KS) DFT wherein the exchange correlation energy functional is expanded to the second order with respect to charge density fluctuations. Augmentation of this method as implemented in DFTB+ has allowed for the variationally optimized calculation of spin-purified excited state properties with application in spectral prediction and efficient description of large excited systems. Selection of KS spin orbitals based on the character of the excited state, 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 result in the spin purified virtual state of the system revealing its energy and optimized geometry. The ability to describe properties of an excited system along a molecular dynamics trajectory allows for simulation of spectroscopies used to describe photophysical relaxation. The electronic transition dipole moment (TDM) is a useful property to describe as it dictates the intensity of electronic transition, corresponding to the intensity of spectral peaks. The TDM is also useful in deriving rates of energy transfer in excited donor-acceptor systems. Calculation of TDMs within a DFTB framework is complicated by the fact that ground and excited states though separately orthogonal are not mutually so, therefore a corresponding orbital transformation must be applied to the molecular orbitals of the ground and excited-state to ensure orthogonality. Benchmarking of this work will be directly compared to similar calculations in EOM-CCSD and TD-DFT, both methods noted for their level of accuracy that scales with their computational expense. Successful porting of these calculations into DFTB+ creates an accessible method for high throughput screening of large photoactive systems with application in alternative energy solutions.