1,721,088 research outputs found
Calculation of the photoabsorption of HF in the Vacuum UV
No full textThe photoabsorption cross section of the HF molecule up to 12 eV arising from the X-->A transition is computed by a large one-electron basis set of atomic natural orbitals and highly correlated wavefunctions. The quality of the results is checked by the accordance of the transition probabilities evaluated both in the dipole length and velocity gauges. Cross sections within an accuracy of 7% are obtained by multireference extended CI with selected CAS-SCF reference states. Comparison with two experimental results, in large disagreement with each other, does not permit an assessment of which experiment is more reliable
Performance of polynomial Gaussian functions in describing the molecular electronic continuum
No full textThe continuum molecular orbitals arising from L-2 calculations using special polynomial Gaussian functions are accurately tested to probe their capability in producing accurate photoemission cross sections. The molecular potential is represented by the local X alpha approximation, which permits a comparison with numerically integrated (exact) orbitals. Several strong anisotropic molecules are taken into account to check the flexibility of the L-2 bases in the presence of strong attractive potentials. This work shows that for adequate choices of Gaussian functions, phase shifts may be estimated with reasonable accuracy while the errors in the continuum transition probabilities are within 2-3% in the more unfavourable cases. Therefore, the proposed basis sets appear to be suitable for the description of the electronic continuum in molecular photoionization calculations
BASIS SET AND GAUGE DEPENDENCE OF ABINITIO RADIATIVE LIFETIMES FOR THE A 2-SIGMA+ STATE OF THE HF+ MOLECULE
No full textAb initio calculations of the Franck-Condon factors for ionization of HF and DF in the X 2Pi and A 2Sigma+ states
No full textTheoretical study of the dissociation of HF+ in the B 2Sigma+ state by quantum mechanical methods
No full textThe dissociative pathway of the HF+ molecular ion, initially in its B (2)SIGMA+ electronic state, is studied by a full quantum-mechanical technique. The vibronic time-dependent wave function is expanded on the twelve lowest (2)SIGMA+ electronic states computed by a limited configuration-interaction calculation. The nuclear functions are projected on a monodimensional grid and the time-evolution operator is represented by its (1,1) Pade approximant. The calculations are performed both in the adiabatic and in a semidiabatic representation of the electronic states. The decay pattern shows strong vibronic interactions often involving several states at a time. The results are compared with those obtained in a previous calculation, where the nuclear motion was treated by a classical trajectories approach
Theoretical study of the dissociation of the HF+ and DF+ ions in the B 2Sigma+ state by classical trajectories
No full textThe Hartree-Fock Method
No full textStarting from the general context of the time-independent Schrödinger equation, the Hartree–Fock method is presented in a didactic way in order that nonexpert readers can understand some subtle problems arising along the development of the theory. Emphasis is given to the accordance of Slater determinants with the first principles of quantum mechanics and to rationalize in an intuitive way some properties of the Hartree–Fock wave function. The projected equations and Koopmans' theorem are discussed in some detail and the restricted and unrestricted treatments are briefly presented
Calculation of the differential photoionization cross section of HF
No full textCross sections, photoelectron angular distribution parameters and branching ratios for the ionization of the valence 1 pi, 3 sigma and inner-valence 2 sigma shells of hydrogen fluoride have been calculated in the Random Phase Approximation (RPA). The computational procedure is based on the K-matrix technique and projection on basis sets of L(2) functions to solve the RPA equations for the three coupled ionization channels in a way that recovers the electronic continuum degeneracy
Differential photoionization cross section calculations for HI using the random-phase approximation with L(2) basis functions
No full textThe photoionization cross sections and asymmetry parameters of the three main valence ionization processes in HI, corresponding to the formation of, respectively, 6 pi, 11 sigma, and 10 sigma holes, were calculated in the random-phase approximation (RPA). Our particular computational procedure, based on solving the integral equation for the half on the shell K-matrix upon a grid of points supplied by an L(2) basis set calculation, affords recovery of the electronic continuum degeneracy of the final states. This makes it possible to compute the differential ionization cross section at any energy up to the fourth ionization threshold, allowing for the interaction of the three channels considered. The total cross section obtained by applying the Stieltjes imaging procedure to the discrete spectrum yielded by the RPA is also reported. (C) 1996 John Wiley & Sons, Inc
Calculation of the differential photoionization cross-section of PH3
No full textCross-sections, photoelectron angular distribution parameters and branching ratios for the ionization of the outer-valence 5a(1), 2e and inner-valence 4a(1) shells of phosphine have been calculated up to a photon energy of 90 eV. Ab-initio calculations have been performed, by the K-matrix technique and projection on basis sets of L-2 functions, in the random phase approximation for the three coupled ionization channels. The theoretical results, compared with the available experimental data and with recent semi-empirical calculations, show a quantitative agreement with the experiment. (C) 1999 Elsevier Science B.V. All rights reserved
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