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Center for Nonlinear Studies |
The new release of DFTB+ as a density-functional (DFT)-based approach, combining DFT-accuracy and Tight-Binding (TB) efficiency, is reported; http//:www.dftb.org. Methodological details and recent extensions to improve reliability and accuracy will be described. Advanced functions include spin degrees of freedom, time dependent methods for excited states, non-adiabatic electron-ion dynamics and quantum transport calculations under open boundary conditions using non-equilibrium Green´s function methods. The major focus of the talk will be on the time-dependent DFTB extensions. I am going to present the first real-time atomistic simulation on the quantum dynamics of plasmon excitations in icosahedral silver nanoparticles under strong laser pulses. We identify the emergence of sub-picosecond breathing-like radial oscillations starting immediately after laser pulse excitation, with increasing amplitude as the field intensity increases. The ultrafast dynamic response of nanoparticles to laser excitation points to a new plasmon assisted mechanism rather than longer time-scale equilibrium electron-phonon scattering previously assumed. The TD-DFTB implementation in real time domain also allow to simulate transient absorption spectra (TAS) fully atomistically. When this technique is applied to the study of ultrafast dynamics of Soret-excited zinc(II)-tetraphenylporphyrin in the sub-picosecond time scale, quantum beats in the transient absorption caused by impulsively excited molecular vibrations are observed. As last examople ultrafast electron transfer in P3HT-PBCM organic blends will be demonstrated to become enhanced by the nuclear motion and under open boundary conditions with applied bias.
Host: Sergei Tretiak