Magnetic properties in DKH calculations of electronic g values

Electron paramagnetic resonance (EPR) spectroscopy is a powerful method for investigating interrelations between electronic and structural features of systems with unpaired electrons, such as radicals, coordination compounds and paramagnetic sites in solids [107-109]. Along with the hyperfine coupling constants, the electronic g matrix (often called g tensor ) is the fundamental quantity furnished by EPR spectroscopy. Nevertheless, it was only in the past few years that g tensors attracted significant attention of the research community that deals with high-level quantum chemical calculations [86,110-113]. 

This obvious need for clarifying the relationship between the electronic and geometric stmcture of paramagnetic systems and their g values nowadays can be met with the help of first-principles quantum chemical methods. A theoretical description of electronic g values, based on a relativistic method which accurately treats spin-orbit interaction even in cases when it is too strong to be considered as a perturbation, will be uniformly applicable to systems with both light and heavy atoms. 

Recently, such universal tools for calculating electronic g matrices of molecular systems in a doublet state were developed, implemented, and validated [35,112,116]. These tools employ two-component eigenfunctions from relativistic DF calculations which take spin-orbit interaction into account self-consistent-ly [18,19] (see Section 2.3) in such a formalism, the parameter g is treated as a first-order property with the external magnetic field as the only perturbation, at 

Such a picture change is required when an expectation value of an operator is to be evaluated [117]. This is particularly important in the present case because the odd [118]) operator couples only large to small components. If one invokes the fpFW transformation Uq (Section 2.2), one obtains the approximate electronic Zeeman Hamiltonian  

Finally, the presently implemented formula for the derivative of with respect to the field components B reads [35]  

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