Calculation of molecular <i>g</i>-tensors by sampling spin orientations of generalised Hartree-Fock states

The variational inclusion of spin-orbit coupling in self-consistent field (SCF) calculations requires a generalised two-component framework, which permits the single-determinant wave function to completely break spin symmetry. individual components molecular g-tensor are commonly obtained from separate SCF solutions that align magnetic moment along one three principal tensor axes. However, this strategy raises question if energy differences between relevant, or how convergence is achieved axis system not determined by present work resolves these issues simple two-step procedure akin generator coordinate method (GCM). First, few Hartree Fock (GHF) converged, applying, where needed, constraint orientation magnetic-moment vector. Then, superpositions GHF determinants formed through non-orthogonal configuration interaction. This yields Kramers doublet for calculation complete g-tensor. Alternatively, systems with weak effects, diagonalisation basis spanned rotations single determinant affords qualitatively correct g-tensors eliminating errors related contamination. For small first-row molecules, approaches evaluated against experimental data and full interaction results. It further demonstrated two (a fictitious tetrahedral CH4+ species, CuF4(2-) complex) GCM strategy, contrast alternative mean-field methods, can correctly describe splitting orbitally-degenerate ground states, causes large g-shifts may lead negative g-values.