We present a theoretical approach for the simulation of time-resolved harmonic spectra, including the effect of nuclear dynamics, which is applicable to complex systems involving many nuclear degrees of freedom. The method is based on the combination of our semiclassical field-induced surface hopping approach for the treatment of laser-induced nuclear dynamics with the time-dependent density functional theory for electron dynamics. We apply our method to the simulation of ultrafast nonadiabatic dynamics and time-resolved harmonic spectra in small silver clusters (Ag 2 and Ag 8 ), which exhibit discrete molecularlike electronic transitions. We demonstrate that the harmonic signal is highly sensitive to the nuclear dynamics and thus can be used as a probe of coupled electron-nuclear dynamics, which is complementary to common pump-probe methods such as time-resolved photoelectron spectroscopy. Our simulations allowed us also to determine the mechanism and the time scale of nonradiative relaxation in the "magic" Ag 8 cluster and have provided a fundamental insight into ultrafast dynamics of metal nanoclusters in the size regime where "each atom counts." The excited-state dynamics of Ag 8 involves an isomerization process from the initial structure with T d symmetry to the quadratic antiprism structure with D 4d symmetry which takes place on a time scale of ∼600 fs and is clearly identified in a time-resolved harmonic signal. Our theoretical approach is generally applicable for the prediction of time-resolved harmonic spectra in complex systems with many nuclear degrees freedom and should serve to stimulate new ultrafast experiments utilizing harmonic signals as a probe for nonadiabatic processes in molecular systems.PHYSICAL REVIEW A 83, 033408 (2011)where χ (N) I (R,t) and χ (N−1) J (R,E,t) represent the nuclear wave packet in the bound and continuum states, respectively. 033408-4 SIMULATION OF LASER-INDUCED COUPLED ELECTRON-. . . PHYSICAL REVIEW A 83, 033408 (2011) (N) I (r; R) are the eigenfunctions of the N-electron Hamiltonian, while the antisymmetrized product A[ (N−1) J (r; R)φ J (E)] represents the continuum eigenfunctions of the combined ion-free electron Hamiltonian. In this product (N−1) J (r; R) is the J th cationic state and φ J (E) is a free electron scattering state. The summation extends over the whole range of singly ionized states. The wave-function ansatz in Eq. (17) can be inserted in the full electron-nuclear TDSE including the coupling to the electric field and a set of equations for the time evolution of the continuum portion of the nuclear wave packet of the ionized system χ (N−1) J (R,E,t) can be derived as ihχ (N−1) J (R,E,t) = T + E (N−1) J + E χ (N−1) J (R,E,t) − I ε(t) · µ I J (R,E)χ (N) I (R,t). (18) The semiclassical limit of this equation can be obtained by reducing the wave packet χ (N−1) J (R,E,t) to swarms of trajectories, as described previously [18]. This yields a set of equations for the time evolution of the amplitudes c (N−1) J (E,t) associated with each trajectory of a continu...

We have investigated the ultrafast electronic relaxation of Au − 7 using time-resolved photoelectron spectroscopy combined with first-principles simulations of the excited-state dynamics. Unlike previous findings, which have demonstrated molecularlike excited-state relaxation in Au − 7 at low excitation energy (1.56 eV), we show here that excitation with 3.12 eV leads to bulklike electronic relaxation without a considerable change of geometry. The experimental findings are fully supported by theoretical simulations, which reveal a bulklike electron-hole relaxation mechanism in a far band-gap cluster. Our findings demonstrate that small gold clusters in the sub-nm size range can exhibit either molecularlike or bulklike properties, depending on the excitation energy.

We present a theoretical approach for the simulation of the optical response and light propagation in aggregates and in ordered arrays of small noble-metal clusters with discrete electronic structure. We construct the Hamiltonian for the aggregate system based on the time-dependent density functional theory electronic states of the individual subunits and describe the interaction between them using the dipole approximation. The time evolution of the aggregate under the influence of the external electric field is obtained from the numerical solution of the timedependent Schrödinger equation with the coupled excitonic Hamiltonian. For each subunit, the time-dependent dipole moment is calculated using the reduced density matrix formalism. Such quantum-mechanically determined dipole moments are used to simulate the spatiotemporal distribution of the electric field produced by the array. Additionally, we introduce an approximate self-consistent iterative approach to treat arrays consisting of many subunits which are of interest in the context of nanoplasmonics, nano-optical applications, and development of light-harvesting materials. The developed methodology is illustrated first on the example of Ag 2 and Ag 8 cluster pairs. Subsequently, light propagation in a triangular-shaped array consisting of six Ag 8 clusters is simulated.

Metal−organic hybrid structures have been demonstrated to be a versatile platform to study primary aspects of light−matter interaction by means of emerging states comprising excitonic and plasmonic properties. Here we are studying the wave-vector-dependent photoexcitations in gold layers covered by molecular films of zinc phthalocyanine and its fluorinated derivatives (F n ZnPc, with n = 0, 4, 8, 16). These layered metal−organic samples show up to four anticrossings in their dispersions correlating in energy with the respective degree of ZnPc fluorination. By means of complementary structural and theoretical data, we attribute the observed anticrossings to three main scenarios of surface plasmon coupling: (i) to aggregated α-phase regions within the F n ZnPc layers at 1.75 and 1.85 eV, (ii) to a coexisting F 16 ZnPc β-polymorph at 1.51 eV, and (iii) to monomers, preferentially located at the metal interface, at 2.15 eV. Whereas energy and splitting of the monomer anticrossings depend on strength and average tilting of the molecular dipole moments, the aggregaterelated anticrossings show a distinct variation with degree of fluorination. These observations can be consistently explained by a change in F n ZnPc dipole density induced by an increased lattice spacing due to the larger molecular van der Waals radii upon fluorination. The reported results prove Au/F n ZnPc bilayers a model system to demonstrate the high sensitivity of exciton−plasmon coupling on the molecular alignment at microscopic length scales.

We present a joint theoretical and experimental study of the excited state dynamics in pure and hydrated anionic gold clusters AuWe employ mixed quantum-classical dynamics combined with femtosecond time-resolved photoelectron spectroscopy in order to investigate the influence of hydration on excited state lifetimes and the photo-dissociation dynamics.Gradual decrease of the excited state lifetime with the number of adsorbed water molecules as well as gold cluster fragmentation quenching by two or more water molecules are observed both in experiment and in simulations. Non-radiative relaxation and dissociation in excited states are found to be responsible for the excited state population depletion. Time constants of these two processes strongly depend on the number of water molecules leading to the possibility to modulate excited state dynamics and fragmentation of the anionic cluster by adsorption of water molecules.