1,721,096 research outputs found
Angular dependent time delay near correlation induced Cooper minima
Full text linkWe analyze an angular dependence of the Wigner time delay near the Cooper minimum (CM) of the sub-valent ns shell in argon, krypton and xenon. Such an angular dependence is a result of interplay between the relativistic and correlation effects. The correlation with the outermost np valence shell induces a CM in the sub-valent ns shell which is otherwise CM free. A phase difference between the two spin-orbit split ionization continua Ep 1/2 and Ep 3/2 makes the Wigner time delay angular dependent. Both these effects are accounted for within relativistic formulations of the random phase approximation and the time-dependent density functional theory. Comparison between these two approaches illustrates a very strong sensitivity of the observed effect to the computation detail, especially the account of the ground state correlation
Full Ab Initio Many-Electron Simulation of Attosecond Molecular Pump-Probe Spectroscopy
No full textHere, we present an ab initio approach to full simulation of an attosecond molecular pump-probe experiment. Sequential molecular double ionization by the pump and probe laser pulses with controlled delay is described from first-principles with a full account of the continuum dynamics of the photoelectrons. Many-electron bound-continuum dynamics is simulated using the time-dependent (TD) molecular B-spline algebraic diagrammatic construction (ADC) method. Our calculations give a quantitative prediction about the creation of a coherent superposition of molecular ionic states in the photoionization process and simulate the probe of the ensuing attosecond dynamics by a second ionizing pulse within a single first-principles many-electron framework. We therefore demonstrate the capability to simulate and interpret the results of a prototypical molecular pump-probe experiment of interest in attoscience. As a particular example, we simulate and elucidate the interpretation of a pump-probe experiment in CO2 aimed at measuring strong field-induced hole dynamics via photoionization yields
Photoabsorption and photoionization dynamics study of silicon tetrafluoride in the framework of time-dependent density-functional theory
No full textPhotoionization cross sections and angular distributions of silicon tetrafluoride have been calculated in the
framework of the time-dependent density-functional theory approach. Both valence and inner shell ionizations
have been considered in an extended photon energy range. Calculations have been carried out by using two
different exchange-correlation xc potentials characterized by the correct asymptotic behavior. Theoretical
results obtained with both the van Leeuwen–Baerends and statistical average of orbital potentials SAOP xc
potentials are compared with photoabsorption, photoionization, and electron-scattering experiments as well as
with previous theoretical calculations. It is suggested that even if both xc potentials provide a reasonably good
description of the photoionization dynamics, correlation effects are phenomenologically better accounted for
by the SAOP xc potential. Overall, the good accuracy attained with the linear combination of atomic orbitalstime
dependent density-functional theory method in reproducing the experimental findings for SiF4 makes it a
promising and powerful method for the characterization of the photoionization dynamics from medium and
large-size molecules
Multi-channel dynamics in high harmonic generation of aligned CO₂: ab initio analysis with time-dependent B-spline algebraic diagrammatic construction
Full text linkHere we present a fully ab initio study of the high-order harmonic generation (HHG) spectrum of aligned CO2 molecules. The calculations have been performed by using the molecular time-dependent (TD) B-spline algebraic diagrammatic construction (ADC) method. We quantitatively study how the sub-cycle laser-driven multi-channel dynamics, as reflected in the position of the dynamical minimum in the HHG spectrum, is affected by the full inclusion of both correlation-driven and laser-driven dipole interchannel couplings. We calculate channel-resolved spectral intensities as well as the phase differences between contributions of the different ionization-recombination channels to the total HHG spectrum. Our results show that electron correlation effectively controls the relative contributions of the different channels to the total HHG spectrum, leading to the opening of the new ones (12Πu, 12Σ), previously disregarded for the aligned molecular setup. We conclude that inclusion of many-electron effects into the theoretical interpretation of molecular HHG spectra is essential in order to correctly extract ultrafast electron dynamics using HHG spectroscopy
Accurate Description of Photoionization Dynamical Parameters
Full text linkCalculation of dynamical parameters for photoionization requires an accurate description of the initial and final states of the system, as well as of the outgoing electron. We show that using a linear combination of atomic orbitals B-spline density functional theory (DFT) method to describe the outgoing electron, in combination with correlated equation of motion coupled cluster singles and double Dyson orbitals, gives good agreement with experiment and outperforms other simpler approaches, like plane and Coulomb waves, used to describe the photoelectron. Results are presented for cross-sections, angular distributions, and dichroic parameters in chiral molecules, as well as for photoionization from excited states. We also present a comparison with the results obtained using Hartree-Fock and DFT molecular orbitals selected according to Koopmans' theorem for the bound states
Electron correlation effects in the photoionization of CO and isoelectronic diatomic molecules
No full textThis paper investigates the first sigma satellite band, which is by far the most prominent, in the valence photoelectron spectra for a set of isoelectronic diatomic molecules: carbon monoxide, carbon monosulfide, carbon monoselenide, silicon monoxide and boron monofluoride. In particular, we analyze the effect of the electronic structure, with the change of the atomic pair along the row and column of the periodic table on the position of the satellite peak as well as on the related dynamical observables profiles. For this investigation, highly correlated calculations have been performed on the primary ionic states and the satellite band for all the molecules considered. Cross sections for the primary ionic states, calculated using Dyson orbitals, have been compared with those obtained with Hartree-Fock and Density Functional Theory to probe the impact of the correlation in the bound states on the photoionization observables. Limitations of a simple intensity borrowing mechanism clearly result from the analysis of the satellite state, characterized by different features with respect to the relevant primary states
High-Resolution Inner-Shell Photoabsorption and Dissociation of Ozone
No full textThe total-ion-yield (TIY) spectrum of ozone has been recorded in the K-edge region for the first time with
high photon energy resolution and without significant O2 contamination. Spectral features have been clearly
observed in the high energy region below the two ionization thresholds. The assignment for the core excitation
processes from the “terminal” and “central” oxygen atoms, given for the first time in the whole spectral
range, is based on high level ab initio calculations. The QDPTCI (quasidegenerate perturbation theory
configuration interaction) theoretical approach provided an excitation energy pattern and photoabsorption
oscillator strengths that were found in good agreement with the experimental TIY spectrum. The decay dynamics
of the core excited resonant states is shown to be strongly dependent on the ó/ð antibonding character of the
virtual MO involved in the excitation process
Continuum Electronic States: The Tiresia Code
Full text linkA multicenter (LCAO) B-spline basis is described in detail, and its capabilities concerning affording convergent solutions for electronic continuum states and wavepacket propagation are presented. It forms the core of the Tiresia code, which implements static-DFT and TDDFT hamiltonians, as well as single channel Dyson-DFT and Dyson-TDDFT descriptions to include correlation in the bound states. Together they afford accurate and computationally efficient descriptions of photoionization properties of complex systems, both in the single photon and strong field environments. A number of examples are provided
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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