Quantum Chemical Calculations of EPR Parameters for Transition Metal Complexes

Modern density-functional methods for the calculation of electronic g-tensors have been implementedwithin the framework of the deMon code. All relevant perturbation operators are included. Particular emphasishas been placed on accurate yet efficient treatment of the two-electron spin-orbit terms. At an all-electronlevel, the computationally inexpensive atomic mean-field approximation is shown to provide spin-orbitcontributions in excellent agreement with the results obtained using explicit oneand two-electron spin-orbitintegrals. Spin-other-orbit contributions account for up to 25-30% of the two-electron terms and may thusbe non-negligible. For systems containing heavy atoms we use a pseudopotential treatment, wherequasirelativistic pseudopotentials are included in the Kohn-Sham calculation whereas appropriate spin-orbitpseudopotentials are used in the perturbational treatment of the g-tensors. This approach is shown to provideresults in good agreement with the all-electron treatment, at moderate computational cost. Due to the atomicnature of both mean-field all-electron and pseudopotential spin-orbit operators used, the two approaches mayeven be combined in one calculation. The atomic character of the spin-orbit operators may also be used toanalyze the contributions of certain atoms to the paramagnetic terms of the g-tensors. The new methods havebeen applied to a wide variety of species, including small main group systems, aromatic radicals, as well astransition metal complexes.