Simulation of x-ray absorption near edge spectra of electronically excited ruthenium tris-2,2'-bipyridine

The L(3) edge x-ray absorption near edge spectrum (XANES) of the ground electronic state and the metal to ligand charge transfer state of ruthenium tris-2,2(')-bipyridine is calculated. The final valence states and energies in the presence of the photoelectron and core hole, and the corresponding transition intensities are computed using time dependent density functional theory with the Becke three-parameter density functional with the Lee-Yang-Parr correlation functional. Calculations show a valence shift of the primary XANES peak and the appearance of the new XANES transition to the hole created by the optical excitation, in agreement with experiment [M. Saes, C. Bressler, R. Abela, D. Grolimund, S. L. Johnson, P. A. Heimann, and M. Chergui, Phys. Rev. Lett. 90, 047403 (2003)].     

Exciton annihilation on dendrimeric trees

Exciton-exciton annihilation on Cayley tree like dendrimer molecules are investigated via Monte Carlo simulations. Annihilation reaction of the type A+A→0 is considered to calculate the exciton density decay for multiexciton diffusion on dendrimers. Exciton density decays as a power law with a continuously varying exponent in a linear potential. For the case of realistic nonlinear potential of phenylacetylene dendrimers (Phys. Rev. Lett. 77 (1998) 4656) the excitons accumulate around the free energy minimum and annihilate each other quickly.     

Modelling one-dimensional driven diffusive systems by the Zero-Range Process

In order to characterize networks in the scale-free network class we study the frequency of cycles of length h that indicate the ordering of network structure and the multiplicity of paths connecting two nodes. In particular we focus on the scaling of the number of cycles with the system size in off-equilibrium scale-free networks. We observe that each off-equilibrium network model is characterized by a particular scaling in general not equal to the scaling found in equilibrium scale-free networks. We claim that this anomalous scaling can occur in real systems and we report the case of the Internet at the Autonomous System Level.Received: 15 January 2004, Published online: 14 May 2004PACS: 89.75.-k Complex systems - 89.75.Hc Networks and genealogical trees     

Probing anomalous relaxation by coherent multidimensional optical spectroscopy

We propose to study the origin of algebraic decay of two-point correlation functions observed in glasses, proteins, and quantum dots by their nonlinear response to sequences of ultrafast laser pulses. Power-law spectral singularities and temporal relaxation in two-dimensional correlation spectroscopy signals are predicted for a continuous time random walk model of stochastic spectral jumps in a two-level system with a power-law distribution of waiting times psi(t) approximately t;{-alpha-1}. Spectroscopic signatures of stationary ensembles for 1相似文献   

Anomalous lineshapes and aging effects in two-dimensional correlation spectroscopy

Multitime correlation functions provide useful probes for the ensembles of trajectories underlying the stochastic dynamics of complex systems. These can be obtained by measuring their optical response to sequences of ultrashort optical pulse. Using the continuous time random walk model for spectral diffusion, we analyze the signatures of anomalous relaxation in two-dimensional four wave mixing signals. Different models which share the same two point joint probability distribution show markedly different lineshapes and may be distinguished. Aging random walks corresponding to waiting time distributions with diverging first moment show dependence of 2D lineshapes on initial observation time, which persist for long times.     

Ab initio simulations of two‐dimensional electronic spectra: The SOS//QM/MM approach

Two‐dimensional electronic spectroscopy (2DES) is a cutting‐edge technique for investigating with high temporal resolution energy transfer, structure, and dynamics in a wide range of systems in physical chemistry, energy sciences, biophysics, and biocatalysis. However, the interpretation of 2DES is challenging and requires computational modeling. This perspective provides a roadmap for the development of computational tools that could be routinely applied to simulate 2DES spectra of multichromophoric systems active in the UV region (2DUV) using state‐of‐the‐art ab initio electronic structure methods within a quatum mechanics/molecular mechanics (QM/MM) scheme and the sum‐over‐states (SOS) approach (here called SOS//QM/MM). Multiconfigurational and multireference perturbative methods, such as the complete active space self‐consistent field and second‐order multireference perturbation theory (CASPT2) techniques, can be applied to reliably calculate the electronic properties of multichromophoric systems. Hybrid QM/MM method and molecular dynamics techniques can be used to assess environmental and conformational effects, respectively, that shape the 2D electronic spectra. DNA and proteins are important biological targets containing UV chromophores. We report ab initio simulation of 2DUV spectra of a cyclic tetrapeptide containing two interacting aromatic side chains, a model system for the study of protein structure and dynamics by means of 2DUV spectroscopy. © 2013 Wiley Periodicals, Inc.     

Dynamics of simple computer networks

We consider a simple two-dimensional layered automaton. Each processor in the automaton performs the same nonlinear, thresholdlike operation (so that the row-to-row evolution of the array can also be seen as the time development of a one-dimensional automaton). One row of the machine is reserved for input, another is singled out as output. We study the output space in detail, as restricted by the very wiring of the array, enumerating the output configurations, and characterizing them statistically. We demonstrate that input configurations flow to a set of zero measure in output space. The variations in output that are to be expected when input is subjected to perturbations are also examined.     

Manipulating valence and core electronic excitations of a transition-metal complex using UV/Vis and X-ray cavities

We demonstrate how optical cavities can be exploited to control both valence- and core-excitations in a prototypical model transition metal complex, ferricyanide ([Fe(iii)(CN)₆]³⁻), in an aqueous environment. The spectroscopic signatures of hybrid light-matter polariton states are revealed in UV/Vis and X-ray absorption, and stimulated X-ray Raman signals. In an UV/Vis cavity, the absorption spectrum exhibits the single-polariton states arising from the cavity photon mode coupling to both resonant and off-resonant valence-excited states. We further show that nonlinear stimulated X-ray Raman signals can selectively probe the bipolariton states via cavity-modified Fe core-excited states. This unveils the correlation between valence polaritons and dressed core-excitations. In an X-ray cavity, core-polaritons are generated and their correlations with the bare valence-excitations appear in the linear and nonlinear X-ray spectra.

We demonstrate how optical cavities can be exploited to control both valence- and core-excitations in a prototypical model transition metal complex, ferricyanide ([Fe(iii)(CN)₆]³⁻), in an aqueous environment.     

Ab initio calculation of the He2 A 1Σ u +└X 1Σ g + absorption spectrum

The absorption spectrum of helium gas near 600 Å, assigned to the A ¹Σ _u ⁺└X ¹Σ _g ⁺ transition in He₂, is calculated at 77 K. The excited state potential is taken from a recent ab initio calculation. The theoretical spectrum shows well-defined bands, corresponding to different vibration levels of the A state, with diffuse rotational structure, in agreement with experiment. Fairly good quantitative agreement with Tanaka and Yoshino's measured spectrum is obtained, except for the somewhat too large separation between calculated vibrational bands, probably due to the theoretical potential for the A state rising too steeply at small inter-nuclear separation. Rotational constants derived from the calculated and experimental spectra are in good agreement. It is shown that they are significantly smaller than actual rotational constants of the upper state.