Perspective on Kramers symmetry breaking and restoration in relativistic electronic structure methods for open-shell systems
- Univ. of Washington, Seattle, WA (United States)
Without rigorously symmetry constraints, solutions to approximate electronic structure methods may artificially break symmetry. In the case of relativistic electronic structure, if time-reversal symmetry is not enforced in calculations of molecules not subject to a magnetic field, it is possible to artificially break Kramers degeneracy in open shell systems. This leads to a description of excited states that may be qualitatively incorrect. Despite this, different electronic structure methods to incorporate correlation and excited states can partially restore Kramers degeneracy from a broken symmetry solution. For single-reference techniques, the inclusion of double and possibly triple excitations in the ground state provides much of the needed correction. Formally, however, this imbalanced treatment of the Kramers-paired spaces is a multi-reference problem, and so methods such as complete-active-space methods perform much better at recovering much of the correct symmetry by state averaging. Using multi-reference configuration interaction, any additional corrections can be obtained as the solution approaches the full configuration interaction limit. A recently proposed "Kramers' contamination" value is also used to assess the magnitude of symmetry breaking.
- Research Organization:
- Univ. of Washington, Seattle, WA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
- Grant/Contract Number:
- SC0006863; SC0021100; CHE-1856210; OAC-1663636
- OSTI ID:
- 1714358
- Alternate ID(s):
- OSTI ID: 1657630; OSTI ID: 1870637
- Journal Information:
- Journal of Chemical Physics, Vol. 153, Issue 9; ISSN 0021-9606
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Similar Records
Two-component multi-configurational second-order perturbation theory with Kramers restricted complete active space self-consistent field reference function and spin-orbit relativistic effective core potential
Real-Time Time-Dependent Electronic Structure Theory
Related Subjects
complete-active space self-consistent field
electronic structure methods
full configuration interaction
spin-orbit interactions
degenerate energy levels
coupled-cluster methods
Kramers theorem
multi-reference configuration interaction
particle symmetry
field theory
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS