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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
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Time-Dependent Second-Order Green's Function Theory for Neutral Excitations
Wenjie Dou1,2,3, Joonho Lee4, Jian Zhu1,3
1Department of Chemistry, School of Science, Westlake University, Hangzhou, Zhejiang 310024, China.
Journal of Chemical Theory and Computation
|August 30, 2022
Summary
We introduce a new Green's function theory (GF2) for calculating molecular excited states. This GF2-BSE method accurately predicts excited states, outperforming TDHF and CIS, especially for charge-transfer excitations.
Area of Science:
- Quantum Chemistry
- Theoretical Chemistry
- Computational Chemistry
Background:
- Calculating neutral excited states in molecules is crucial for understanding photochemical and photophysical processes.
- Existing methods like Time-Dependent Hartree-Fock (TDHF) and Configuration Interaction with Singles (CIS) have limitations in accuracy, particularly for certain types of excitations.
Purpose of the Study:
- To develop and present a novel time-dependent second-order Green's function theory (GF2) for accurate calculation of neutral excited states in molecules.
- To evaluate the performance of the new GF2 theory against established computational methods.
Main Methods:
- Derivation of the equation of motion for the lesser Green's function (GF) using the adiabatic approximation to the Kadanoff-Baym (KB) equation.
- Application of the second-order Born approximation for the self-energy.
- Recasting the time-dependent KB equation into a Bethe-Salpeter-like equation (GF2-BSE) in the linear response regime.
- Approximation of the GF2-BSE kernel using the second-order Coulomb self-energy.
Main Results:
- The developed GF2-BSE method demonstrates superior accuracy compared to TDHF and CIS for calculating neutral excited states.
- GF2-BSE shows particular strength in describing charge-transfer excitations.
- The accuracy of GF2-BSE is found to be comparable to CIS with perturbative doubles (CIS(D)) for most tested cases.
Conclusions:
- The time-dependent second-order Green's function theory (GF2-BSE) offers a significant advancement in the accurate computation of molecular excited states.
- GF2-BSE provides a more reliable and accurate alternative to existing methods, especially for challenging excitations like charge-transfer states.
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