Related Experiment Video
Updated: Jun 17, 2026

Spatial Separation of Molecular Conformers and Clusters
Published on: January 9, 2014
Gaunt and Breit two-electron contributions to mean-field transformations and fine structure splitting
Luca Murg1,2, Christopher Lane1, Roxanne M Tutchton1
1Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. rtutchton@lanl.gov.
None:
Materials utilized by novel energy systems are often studied using weakly correlated mean-field theories. However, if these systems incorporate heavy elements, relativistic effects must be included. Therefore, a Kramers unrestricted coupled cluster with singles and doubles excitation formalism within a molecular mean-field exact two-component framework (X2Cmmf) using a four-component Dirac-Hartree-Fock (DHF) reference state is presented. The exact X2Cmmf transformed normal-order Hamiltonian incorporates all one-electron and two-electron (2e) contributions from the Coulomb, Gaunt, and Breit operators and is used with the equation of motion method to calculate the excitation energies of the alkali group of elements. Using this framework, the effects of 2e Gaunt and Breit integrals are studied. Results demonstrate growing contributions from these integrals to the generated X2Cmmf mean-fields and electronic fine structure calculations with increasing atomic number. Overall, this paper outlines the method, its effect within the X2Cmmf approach, and lays the foundation for future theoretical development of relativistic calculations within this framework.
Related Concept Videos
Molecular Orbital Theory II
¹H NMR: Complex Splitting
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Hybridization of Atomic Orbitals II
Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
Hybridization of Atomic Orbitals I
The Aufbau Principle and Hund's Rule

