Accurate multichannel continuum states by a general configuration interaction expansion in aB-spline basis: application to He photoionization

Abstract

We report theoretical calculations of the total and partial cross section and asymmetry parameter for He photoionization up to the N = 3 threshold. Multichannel continuum wavefunctions are obtained via a least squares solution of the Schrödinger equation employing a basis set expansion based on a primitive B-spline radial basis and a general configuration interaction form. This allows use of a mixed full CI and close-coupling expansion in a completely general approach to improve correlation description in the continuum channels. The present algorithm correctly describes the full range of phenomena encountered with full details and a remarkable accuracy both on non-resonant cross sections and resonance structures. An accuracy of better than 0.001 Mb is estimated both on total and partial cross sections, also Fano resonance parameters compare very well with the best methods available based on Hylleraas type wavefunctions and complex coordinate rotation.

Photoionization of helium by attosecond pulses: Extraction of spectra from correlated wave functions

“…By contrast, the more recent calculation by Moccia and Spizzo [67] data by Lindle et al [86]. The present two complementary methods (PSS and Berkeley-ECS) agree, within the graphical resolution, perfectly with each other and with the calculation of Moccia and Spizzo [67] and also of Venuti et al [74]. Thus, it appears that the measurements of the β 2 parameter by Lindle et al between the N = 2 and N = 3 thresholds are consistent with theory.…”

“…Today several efficient methods capable of computing multielectron single-ionization scattering states are available. They include the R-matrix [69], J -matrix [70], K-matrix [71,72], Feshbach projection [73], and inverse iteration [74]. Furthermore, the computational overhead for generating scattering states is easily compensated whenever a large number of different simulations must be carried out, as is the case, e.g., of time-delay scans in pump-probe schemes.…”

Role of broadband-laser-pulse temporal extent in H2+photodissociation

“…To complete the calculation procedure we need to solve the eigenvalue equations for the electronic potentials E g (R) and E u (R) we follow an approach where the system is placed in a spherical box which effectively discretizes the continuum spectrum, a method that has been applied with success in both complex atomic and molecular systems [29,[34][35][36][37][38]. The nuclear eigenstates are then expressed in terms of known B-splines polynomials which, after imposing zero boundary condition at both edges of the spherical box, transforms the problem to a matrix generalized eigenvalue problem, which, by now, can be solved using standard numerical approaches.…”

Theoretical investigations on the dynamical correlation in double excitations of helium by theR-matrix method

“…In Burke and McVicar's calculation [7] in 1965, resonance states other than the normally known plus-minus series appeared. Sequently, atomic theoreticians developed various methods to deal with doubly excited states of helium, including configuration-interaction (CI) methods [56][57][58][59][60], hyperspherical coordinate methods [9,[61][62][63][64][65][66][67][68][69][70][71][72][73][74], close-coupling approximations [7,75,76], R-matrix methods [77][78][79][80][81][82][83][84], complex coordinate method [85][86][87][88][89][90], saddle-point technique [91][92][93][94][95], Feshbach projection formalism [8,[96][97][98]…”