The electronic structure of the primary electron donor D-2A and other pigments in photosynthetic reaction center (RC) of the mutant HM202L of Rhodobacter spheaeroides has been studied with the ab initio DFT method. The mechanism of primary electron transfer in this mutant was studied. the results indicated 1) HOMO of super-molecule D-2A mainly consists of the atomic orbitals of atoms located at the composition unit BChl~L, and its LUMO mainly consists of atomic orbitals of atoms located at the composition unit MBPheo~m. These rsults indicate that there exist internal charge separated states [BChl~L^- - MBPheo~M^+] and [BChl~L^+ - MBPheo~M^-] in the ground state and excited state of super-molecule D-2A, respectively. The positive charge of the D-2A cation completely localizes on the composition unit BChl~L, which is in agreement with the experimental fact. 2) There might be a reaction channel, in which the primary electron transfer reaction may be driven by ABCh a~L^h^* in the HM202L photosynthetic reaction center.

Key words: BACTERIA, CHARGE TRANSFER, ELECTRONIC STRUCTURE, AB INITIO CALCULATION