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Approximate singly excited states from a two-component Hartree-Fock reference
Joshua J Goings1, Feizhi Ding1, Ernest R Davidson1
1Department of Chemistry, University of Washington, Seattle, Washington 98195, USA.
The Journal of Chemical Physics
|October 17, 2015
Summary
The two-component Hartree-Fock (2cHF) method offers superior ground state energies for spin-frustrated molecules. This study explores its application to excited states using new computational methods.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Theoretical Chemistry
Background:
- Relaxing spin symmetry constraints in wave functions yields lower energy mean-field solutions for many molecules.
- The two-component Hartree-Fock (2cHF) method removes spin symmetry constraints, resulting in wave functions that are not eigenfunctions of spin or time-reversal symmetry operators.
- 2cHF is a proven superior mean-field method for calculating ground state energies of spin-frustrated molecules, but its utility for excited states remains uncertain.
Purpose of the Study:
- To investigate the applicability and nature of two-component Hartree-Fock (2cHF) for describing excited states in molecules.
- To implement 2cHF extensions for two prominent excited-state methods: two-component configuration interaction singles and time-dependent Hartree-Fock.
- To compare the performance of these 2cHF-based excited-state methods against unrestricted Hartree-Fock and full configuration interaction benchmarks.
Main Methods:
- Implementation of 2cHF extensions for configuration interaction singles (2cCI-S) and time-dependent Hartree-Fock (2cTDHF).
- Comparison of 2cHF-based excited-state calculations with unrestricted Hartree-Fock (UHF) and full configuration interaction (FCI) methods.
- Application and analysis of these methods to three small molecules exhibiting distinct 2cHF solutions.
Main Results:
- Successful implementation of 2cHF extensions for CI-S and TDHF methods.
- Comparative analysis reveals insights into the behavior and accuracy of 2cHF for excited states.
- Discussion on the characteristics of 2cHF excited-state solutions for the studied molecular systems.
Conclusions:
- The study provides a foundational exploration into the use of 2cHF for excited-state calculations in quantum chemistry.
- Findings contribute to understanding the strengths and limitations of 2cHF in describing molecular excited states.
- The implemented methods offer new avenues for investigating spin-unrestricted electronic structures and excitations.
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