•Angular electronic fluxes yield mechanistic information about charge migration.•A pincerwise motion at the nuclei is observed for the S0 + S2 superposition state.•More valence electrons flow concertedly than for the S0 + S1 superposition state.Recently, it was discovered that excitation of the oriented model benzene from its aromatic electronic ground state S0(1A1g) to the non-aromatic S0+S2(1B1u) superposition state generates negative and positive partial charges on alternating carbon atoms. Subsequently, they vary periodically, due to adiabatic attosecond charge migration AACM. Here, we determine the angular electronic flux that mediates this new type of AACM, by means of quantum dynamics simulations. It is found to be periodic, with period τ¯=590as, and with a pincer motion type pattern such that a total of 1.2 valence electrons flow concertedly between alternating sources and sinks at the carbon nuclei.Download high-res image (88KB)Download full-size image

•Novel simple and robust numerical scheme to solve the hydrodynamical equations of motion.•Separation of particle density in analytical and residual contributions.•Wave packet evolution on anharmonic potential stable over many vibrational periods.A computational method based on the Chebyshev polynomial expansion of the hydrodynamical fields is applied to the quantum trajectory modeling of the one-dimensional vibrational dynamics. The spatial derivatives of the fields are computed using the Chebyshev polynomial recursion, and they are subsequently used to numerically integrate the equations of motion for the fluid particles. The performance of the proposed algorithm is assessed via the comparison with the analytical solutions for the time evolution of a Gaussian wave packet on harmonic potential, and with the results of quantum wave packet propagation on an anharmonic potential. The scheme is found to provide an accurate representation of both the molecular density and the quantum potential, even if low-order truncated expansions are used. The quantum trajectory propagation using the Chebyshev expansion method yields results in close agreement with the corresponding benchmarks, regarding both the time-dependent molecular distributions and the computed observables.

This contribution reports on the first example of laser-driven charge carrier confinement in a solid state quantum dot investigated using a fully atomistic, correlated many-electron ansatz. Specifically, a Ge/Si model nanocrystal is designed to retain the main structural characteristics and excitonic properties of experimentally observed self-assembled pyramidal heterostructures. State-selective laser excitations yielding hole confinement in the Ge nanostructure are simulated using the reduced density matrix variant of the time-dependent configuration interaction method (ρ-TDCI). The degree of carrier localization in the quantum dot is determined by analyzing the correlated one-electron densities from configuration interaction electronic states at a singles level. Additionally, dissipation and pure dephasing are included to treat the coupling of the local core–shell structure with the vibrations of the surrounding silicon matrix. For this purpose, a new microscopic model for these nonadiabatic coupling rates is derived. The results reveal that, despite the presence of dissipation, charge carriers can be efficiently confined by localized optical excitations in the model Ge/Si quantum dot to create long-lived, large permanent dipoles in the nanocrystal.

•The control of adiabatic attosecond charge migration in benzene using rationally designed pulses is demonstrated.•The analysis of transient angular electronic fluxes is performed using wave function based methods.•The electronic phase aquired during the laser preparation step has a marked influence on the charge migration mechanism.We design four linearly x- and y  -polarized as well as circularly right (+) and left (−) polarized, resonant π/2π/2-laser pulses that prepare the model benzene molecule in four different degenerate superposition states. These consist of equal (0.5) populations of the electronic ground state S0(1A1g)S0(1A1g) plus one of four degenerate excited states, all of them accessible by dipole-allowed transitions. Specifically, for the molecule aligned in the xy  -plane, these excited states include different complex-valued linear combinations of the 1E1u,x1E1u,x and 1E1u,y1E1u,y degenerate states. As a consequence, the laser pulses induce four different types of periodic adiabatic attosecond (as) charge migrations (AACM) in benzene, all with the same period, 504 as, but with four different types of angular fluxes. One of the characteristic differences of these fluxes are the two angles for zero fluxes, which appear as the instantaneous angular positions of the “source” and “sink” of two equivalent, or nearly equivalent branches of the fluxes which flow in pincer-type patterns from one molecular site (the “source”) to the opposite one (the “sink”). These angles of zero fluxes are either fixed at the positions of two opposite carbon nuclei in the yz-symmetry plane, or at the centers of two opposite carbon-carbon bonds in the xz-symmetry plane, or the angles of zero fluxes rotate in angular forward (+) or backward (−) directions, respectively. As a resume, our quantum model simulations demonstrate quantum control of the electronic fluxes during AACM in degenerate superposition states, in the attosecond time domain, with the laser polarization as the key knob for control.