(1-A) Ab initio free energy calculation method for electron transfer
Redox (electron transfer) reaction in solution is a vital process in many interesting phenomena such as battery, fuel cell, corrosion, catalysis, photosynthesis. However, few ab initio methods can compute the key properties of redox reactions. We have developed new theoretical approaches, density-functional MD energy gap method, for quantitative calculation of such quantities. Besides, we demonstrated its validity by using model redox reactions of transition-metal complexes in aqueous solution. (Collaboration with J. Blumberger and M. Sprik : Y. Tateyama et al., J. Chem. Phys. 122, 234505 (2005).)
(1-B) Ab initio free energy calculation method for bond breaking/formation coupled to electron transfer
We have developed a DFT-based ab initio free energy calculation method for change of chemical bonds coupled to electron transfer by combining constrained molecular dynamics with the energy gap method for redox free energy. The formulation is derived based on the thermodynamic integration scheme, thus quite general. We have also suggested a special way to choose an efficient scalar constraint for reactions with multiple relevant reaction coordinates. These techniques were applied to water addition along with reduction from the tetrahedral Ru oxoanion to the trigonal-bipyramidal one in aqueous solution. The overall reaction free energy is calculated to be -0.65 eV, which is consistent with the experimental value (-0.59 eV). Free energy surface with respect to bond change and electron transfer as well as probable reaction pathways were obtained as well.(Collaboration with J. Blumberger and M. Sprik : Y. Tateyama et al., J. Chem. Phys. 126, 204506 (2007).)