Associate Prof. Hideaki Takahashi of department of chemistry in Tohoku university is developing theories and methods in theoretical chemistry. The major interest in his early work was focused on the theoretical investigations of the chemical events occurring in condensed environment such as solutions and biological systems. He developed an efficient method (J. Chem. Phys. 121, p.3989, 2004) to compute solvation free energies of a quantum mechanical object in a solution by combining the QM/MM approach with a theory of solutions though a collaborative work with a solution chemist. Further, in the subsequent developments, the method was successfully extended to the calculation of the free energy calculations for oxidationreactions biological systems. Substantial efforts have also been devoted to the parallel implementation of the electronic structure calculation in the QM/MM method, which enables us to perform realistic simulations of large systems. His recent interest is majorly placed on the development of the novel density-functional theory (DFT) for electrons (H. Takahashi, J. Phys. B, 51, No.5, 055102, 2018) which may contribute to solve difficult problems arising in the current DFT.