704 research outputs found

    Spin-dependent localized Hartree-Fock density-functional approach for the accurate treatment of inner-shell excitation of close-shell atoms

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    We present a spin-dependent localized Hartree-Fock (SLHF) density-functional approach for the treatment of the inner-shell excited-state calculation of atomic systems. In this approach, the electron spin-orbitals in an electronic configuration are obtained first by solving Kohn-Sham (KS) equation with SLHF exchange potential. Then a single-Slater-determinant energy of the electronic configuration is calculated by using these electron spin-orbitals. Finally, a multiplet energy of an inner-shell excited state is evaluated from the single-Slater-determinant energies of the electronic configurations involved in terms of Slater's diagonal sum rule. This procedure has been used to calculate the total and excitation energies of inner-shell excited states of close-shell atomic systems: Be, B^+, Ne, and Mg. The correlation effect is taken into account by incorporating the correlation potentials and energy functionals of Perdew and Wang's (PW) or Lee, Yang, and Parr's (LYP) into calculation. The calculated results with the PW and LYP energy functionals are in overall good agreement with each other and also with available experimental and other ab initio theoretical data. In addition, we present some new results for highly excited inner-shell states.Comment: 8 pages and 9 table

    Effective potential study of the rotational excitation of HD by collision with H2

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    This is the published version, also available here: http://dx.doi.org/10.1063/1.430285.The effective potential formalism of Rabitz is extended to a general potential expressed in terms of relative or body‐fixed coordinates and applied to the study of the H2–HD rotationally inelastic collisions. The H2 and HD molecules are treated as rigid rotors and their interaction potential is derived from the H2–H2 potential. Long‐range quadrupole–dipole and quadrupole–quadrupole interactions are also considered. Quantum‐mechanical close‐coupling calculations for three‐dimensional collisions of para‐H2 and ortho‐H2 with HD are performed up to E=0.20 eV. The general features of the rotational excitation cross sections of HD are examined and their sensitivity to certain aspects of the potential are analyzed. In particular, the different roles of the short‐ and long‐range anisotropies are illustrated. It is found that the degree of anisotropy is meaningful only in relation to the magnitude of the ’’effectively’’ spherically symmetric part of potential. The rate constants for pure rotational transitions of HD are presented in the temperature range of 5 to 800 °K. The relation of these results to the quantitative interpretation of the thermal balance of interstellar clouds is pointed out. We have also calculated the rotational relaxation times for the lowest two levels of HD, which could be examined and compared with future sound absorption experiments to assess the accuracy of the H2–HD interaction potential

    Optimization of high-order harmonic generation by genetic algorithm and wavelet time-frequency analysis of quantum dipole emission

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    This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.64.021403.We present an ab initio three-dimensional quantum study of the coherent control of high-order harmonic generation (HHG) processes in intense pulsed laser fields by means of the genetic algorithm optimization of the laser-pulse amplitude and phase. Accurate time-dependent wavefunction and HHG power spectrum are obtained by the time-dependent generalized pseudospectral method and wavelet transform is used to obtain the dynamical phase associated with the dipole-emission time profile. It is shown that “intra-atomic” dynamical phase matching on the sub-optical cycle, attosecond, time scale can be achieved, leading to nearly perfect constructive interference between different returning electronic wave packets and marked improvement in both emission intensity and purity of a given harmonic order

    Role of the electronic structure and multielectron responses in ionization mechanisms of diatomic molecules in intense short-pulse lasers: An all-electron ab initio study

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    This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.70.061402.We present an all-electron ab initio study of multiphoton ionization (MPI) of diatomic molecules in intense laser pulses using the example of N2, O2, and F2, and the theoretical approach of time-dependent density-functional theory with correct long-range potential. The results reveal the importance of the electronic structure and correlated multielectron responses in the ionization mechanism, and make evident inner valence electron contributions to the molecular MPI in strong laser fields

    Complex quasivibrational energy formalism for intense‐field multiphoton and above‐threshold dissociation: Complex‐scaling Fourier‐grid Hamiltonian method

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    This is the published version, also available here: http://dx.doi.org/10.1063/1.460125We present a new complex‐scaling Fourier‐grid Hamiltonian (CSFGH) method for accurate and efficient determination of laser‐induced (multichannel) molecular resonance states without the use of basis set expansions. The method requires neither the computation of potential matrix elements nor the imposition of boundary conditions, and the eigenvectors provide directly the values of the resonance wave functions at the space grid points. The procedure is particularly valuable for excited‐state problems where basis set expansion methods face the challenge. The simplicity and usefulness of the CSFGH method is demonstrated by a case study of the intensity‐dependent c o m p l e x quasivibrational energyeigenvalues (E R , −Γ/2) and eigenvectors associated with multiphoton and above‐threshold dissociation of H+ 2 ions in the presence of intense laser fields (I=1012–1014 W/cm2 )

    Studies of rotational predissociation of van der Waals molecule by the method of complex coordinate

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    This is the published version, also available here: http://dx.doi.org/10.1063/1.439812.A practical method is presented for calculating resonance energies and widths (lifetimes) of metastable states of van der Waals molecules, incorporating the use of complex coordinate transformation and square‐integrable basis functions. The utility of the method is illustrated through a study of the level widths and energies of rotationally predissociating atom–diatom model systems. Satisfactory agreement with previous works was found. Besides involving only bound state calculations and being free from imposement of boundary conditions, the method can be readily extendable to multichannel coupling problems

    Self-interaction-free time-dependent density-functional theory for molecular processes in strong fields:  High-order harmonic generation of H2 in intense laser fields

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    This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.63.023411.We present a self-interaction-free time-dependent density-functional theory (TDDFT) for nonperturbative treatment of multiphoton processes of many-electron molecular systems in intense laser fields. The time-dependent exchange-correlation (xc) energy potential with proper short- and long-range potential is constructed by means of the time-dependent optimized effective potential (OEP) method and the incorporation of an explicit self-interaction-correction (SIC) term. The resulting time-dependent OEP/SIC equations are structurally similar to the time-dependent Hartree-Fock equations, but include the many-body effects through an orbital-independent single-particle local time-dependent xc potential. A numerical time-propagation technique is introduced for accurate and efficient solution of the TDDFT/OEP-SIC equations for two-center diatomic molecular systems. This procedure involves the use of a generalized pseudospectral method for nonuniform optimal grid discretization of the Hamiltonian in prolate spheroidal coordinates and a split-operator scheme in the energy representation for the time development of the electron orbital wave functions. High-precision time-dependent wave functions can be obtained by this procedure with the use of only a modest number of spatial grid points. The theory is applied to a detailed study of high-order harmonic generation (HHG) processes of H2 molecules in intense pulsed laser fields. Particular attention is paid to the exploration of the spectral and temporal structures of HHG by means of the wavelet time-frequency analysis. The results reveal striking details of the spectral and temporal fine structures of HHG, providing new insights regarding the detailed HHG mechanisms in different energy regimes