(A) Real time propagation TDDFT for photoexcitation induced electron-nucleus dynamics
Using a formalism based on the real-time propagation time-dependent density functional theory (RTP-TDDFT), we have investigated the mechanisms of the photoinduced structural transformations of molecular systems on the femtosecond scale. We have shown for the first time that the RTP-TDDFT formalism can well reproduce the vibration frequencies in the excited state. This indicates the adequate accuracy of our method based on RTP-TDDFT for the shape of the excited-state PES, which is crucial for study on excited states dynamics. (Collaboration with N. Oyama, T. Ohno, Y. Miyamoto : Y. Tateyama et al., J. Chem. Phys. 124, 124507 (2006).)
(B) Nonadiabatic couplings based on TDDFT-LR
Most ab initio electronic structure theories are based on the Born-Oppenheimer approximation to separate electronic and nuclear motions. This approximation is known to break down in photochemical processes, which are inherently nonadiabatic, i.e., they involve (avoided) crossings of different electronic states and the nonadiabatic couplings (NACs) become the central quantity. Due to the lack of many-body wavefunctions in TDDFT, calculation of NACs was thought conceptually difficult. Recently we have presented an efficient TDDFT method by utilizing TDDFT-LR, which not only gives a rigorous formula of NACs from TDDFT but also achieves good accuracy when combined with the use of modified linear response theory. Although there are still some challenges to be considered, the efficiency of our methods suggests that they would be potentially applied for the computational design of photochemical reactions. (Collaboration with O. Sugino, H. Hirai and Y. Tateyama: C. Hu, H. Hirai, and O. Sugino, J. Chem. Phys. 127, 064103 (2007); C. Hu, H. Hirai, and O. Sugino, J. Chem. Phys. 128, 154111 (2008); C. Hu, O. Sugino, and Y. Tateyama, to be published. )
(C) TDDFT modified linear response theory for accurate prediction of excitation energies
Time-dependent density functional theory (TDDFT) has become a standard tool for calculating excited state properties. However, for certain types of electronic excitations, conventional TDDFT is known to give inaccurate results, which had been attributed to the insufficiency of exchange-correlation functionals, such as the widely used local density approximation (LDA). To improve TDDFT performance within LDA, a modified linear response (MLR) scheme was recently proposed, in which the responses from not only the ground state (the fraction q of excited electron is 0), but also the intermediate excited states ( 0(D) Linear-response TDDFT for excitation in condensed systems
We're doing researches using the linear response formalism of TDDFT to calculate the excited states and the absorption spectra in condensed systems.(Collaboration with L. Bernasconi, M. Sprik, T. Otsuka.)