Efficient electron dynamics with the planewave-based real-time time-dependent density functional theory: Absorption spectra, vibronic electronic spectra, and coupled electron-nucleus dynamics

摘要

The electron dynamics with complex third-order Suzuki-Trotter propagator (ST _3) has been implemented into a planewave (PW) based density functional theory program, and several applications including linear absorption spectra and coupled electron-nucleus dynamics have been calculated. Since the ST _3 reduces the number of Fourier transforms to less than half compared to the fourth-order Suzuki-Trotter propagator (ST _4), more than twice faster calculations are possible by exploiting the ST _3. We analyzed numerical errors of both the ST _3 and the ST _4 in the presenceabsence of an external field for several molecules such as Al _2, N _2, and C _2H _4. We obtained that the ST _3 gives the same order of numerical errors (10 ~(-5) Ry after 100 fs) as the ST _4. Also, the time evolution of dipole moments, hence the absorption spectrum, is equivalent for both ST _3 and ST _4. As applications, the linear absorption spectrum for an ethylene molecule was studied. From the density difference analysis, we showed that the absorption peaks at 6.10 eV and 7.65 eV correspond to the → 4a _g and → excitation bands, respectively. We also investigated the molecular vibrational effect to the absorption spectra of an ethylene molecule and the dynamics of a hydrogen molecule after the → transition by formulating coupled electron-nucleus dynamics within the Ehrenfest regime. The trajectory of nuclei follows the excited state potential energy curve exactly.