Induced spin symmetry breaking with constrained SCF methods and its effects on symmetry restoration

The practical treatment of systems with unpaired/localized electron spins remains a challenge in electronic structure theory. Typically, such calculations require computationally intensive multi-determinantal methods. The alternative use of more efficient unrestricted Hartree-Fock or Kohn-Sham density functional theory (DFT) methods for approximating such systems with a single determinant often leads to spontaneous spin symmetry breaking. Though these symmetry-broken states can be corrected using spin projection models, it may be difficult to locate a broken-symmetry self-consistent field solution (SCF). In this presentation, we investigate using induced symmetry breaking with constrained SCF, followed by spin projection, as an approach to model open-shell systems.