Calculation of the G-tensor of electron paramagnetic resonance spectroscopy using gauge-including atomic orbitals and density functional theory

An implementation of the g-tensor of electron paramagnetic resonance (EPR) spectroscopy is presented. This implementation is based on density functional theory (DFT) and the use of gauge-including atomic orbitals (GIAO). Contributions from the spin-other-orbit operators are neglected, while all the other relevant perturbation operators are included. The new method is an extension of an existing DFT-GIAO program package for the calculation of the chemical shift of nuclear magnetic resonance spectroscopy; full use is made of the conceptual analogy between the g-tensor and the chemical shift, The new program is applied to various small radicals. The agreement of calculated and experimental g-tensors is good for radicals of first-row elements; experimental trends are generally well reproduced, The quality of calculated results is worse if the scheme is applied to compounds of heavier elements. Possible reasons for these apparent shortcomings of the method are discussed.