Bacteriochlorophyll a radical cation and anion—calculation of isotropic hyperfine coupling constants by density functional methods

Abstract

The geometries of the bacteriochlorophyll a doublet radical cation and anion have been optimized employing the BLYP density functional and the DZVP double zeta basis set, augmented by diffuse functions for the anion. Isotropic hyperfine coupling constants (hfcs) from single point calculations applying the BLYP, B88-P86, PW91-PW91, B88-PW91, B3LYP, B1LYP and BHANDH functionals in combination with the EPR-II basis set are reported and compared with the experimental results. The influence of minor conformational changes on the calculated hfcs was estimated for the radical cation. Furthermore, hfcs for the radical cation coordinated by two water molecules have been determined. It is concluded that the B3LYP/EPR-II//BLYP/DZVP level of theory is especially well suited for the calculation of hfcs of hydrogens and other magnetic nuclei.