Since the traditional time-dependent density functional theory (TDDFT) method can not deal with large complex system,two body fragment molecular orbital method coupled with time-dependent density functional theory (FMO2-TDDFT) method was employed to research the excited energy of uracil in water solution. The results show that the lowest excited energies S1 and S2 obtained from FMO2-TDDFT are quite well agreement with values of TDDFT calculations. The effects of the basis set on the excited energies also were investigated in these two different calculations. The results show that the S1 energies from FMO2-TDDFT and traditional TDDFT increase while S2 energy values decrease with the increasing of polar functions in basis set. In addition, the excited state structure of supermolecules around the center of uracil was calculated by FMO and TDDFT. The results show that FMO2-TDDFT has some advantages in calculating the lowest excited state in the large system.

time-dependent density functional theory(TDDFT); uracil; solvation; fragment molecular orbital method (FMO)