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

The geometries of the bacteriochlorophyll a doublet radical cation and anio n have been optimized employing the BLYP density functional and the DZVP do uble zeta basis set, augmented by diffuse functions for the anion. Isotropi c hyperfine coupling constants (hfcs) from single point calculations applyi ng the BLYP, B88-P86, PW91-PW91, B88-PW91, B3LYP, B1LYP and BHANDH function als 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, hfc s for the radical cation coordinated by two water molecules have been deter mined. 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 m agnetic nuclei.