Calculations of hyperfine coupling constant of copper(II) in aqueous environment. Finite temperature molecular dynamics and relativistic effects

The presented paper is focused on the calculation of hyperfine coupling constants (HFCC) of Cu2+ ion in water environment. To simulate the conditions of the electron paramagnetic resonance (EPR) experiment in aqueous phase, molecular dynamics using the density functional theory (DFT) was employed. In total three different functionals (BLYP, B3LYP, M06) were employed for studying their suitability in describing coordination of Cu2+ by water molecules. The system of our interest was composed of one Cu2+ cation surrounded by a selected number (between thirty and fifty) of water molecules. Besides the non-relativistic HFCCs (Fermi contact terms) of Cu2+ also the four-component relativistic HFCC calculations are presented. The importance of the proper evaluation of HFCCs, the inclusion of spin-orbit term, for Cu2+ containing systems (Neese, J. Chem. Phys. 118, 3939 2003; Almeida et al., Chem. Phys. 332, 176 2007) is confirmed at the relativistic four-component level of theory.