Posts Tagged ‘close-coupling’

STSM by Tor Kjellsson, Stockholm University (SE) with  Luca Argenti and Fernando Martín, Universidad Autonoma de Madrid (ES)
On May 4th, 2014 (19 days)
From SWEDEN to SPAINSU_logo UAM_logo

Time-dependent atomic photoionisation with a Multi-Configuration-Hartree-Fock close-coupling approach

The most critical aspect in understanding electronic motion in matter is the phenomenon called correlation – the collective dynamics of the electrons by which they manage to lower the total energy of the system by avoiding each other. While being of utmost interest to understand, correlation is generally computationally demanding to describe. To account for it during a dynamic process such as ionization is particularly challenging and this problem is the focus of the program package currently being developed in Stockholm and Madrid in collaboration. The program will eventually be able to solve the time-dependent Schrödinger equation (TDSE) for arbitrary manyelectron atoms under the action of pulsed fields and builds on a multi-reference Hartree-Fock close-coupling ansatz.
The main objectives that were carried out during the present STSM were to test the recently added parallel solver as well as implementing an analyser for the output from it. For this analyser we wrote a program that calculates the partial photoelectron spectra dP
/dE, dependent on the  symmetry and the ionization channel index, of the wave packets generated by the TDSE program, based on the projection on a set of scattering states. The scattering states are obtained in terms of a discretized solution to the multi-channel Lippmann-Schwinger equation.
The analyser was successfully tested on helium against a separate two-active-electron program that is known to work correctly.
With these additions a large step towards finalizing the program was taken. When ready, the program will be able to give a theoretical description of realistic attosecond pump-probe experiments that quantitatively accounts for the parent-ion rearrangement during a photoionization event.

stsm-SU-UAMSTSM by  Eva Lindroth and Tor Kjellsson, Stockholm University with Luca Argenti and Fernando Martín, Universidad Autonoma de Madrid
On November 15th, 2013 (7 days)


Time-dependent atomic photoionisation with a Multi-Configuration-Hartree-Fock close-coupling approach

This STSM concerned the collaboration between the COST nodes in Stockholm and Madrid to build a new program to solve the timedependent Schrodinger equation (TDSE) for  arbitrary poly-electronic atoms under the action of pulsed fields.

The program under  construction extends a Multi-Con guration-Hartree-Fock (MCHF) atomic-structure package to include the coupling to an ionized electron. It is based on close-coupling ionization states built from MCHF parent-ion states coupled to radial B-splines. Prior to the STSM, the package could already reproduce photoionization cross sections for arbitrary atoms with both the initial bound state and the final continuum states described
at the MCHF level as detailed in a recent publication [Carette, Dahlstrom, Argenti
and Lindroth 2013 Phys. Rev. A 87 023420].

As a result of the STSM:

  • The inclusion of the K-matrix package for the calculation of multichannelsingle-ionisation scattering states to resolve energetically and angularly the partial photoelectron spectra encoded in the electronic wave packetsobtained from simulations of pump-probe experiments on atoms was started. A similar integration technique was already successfully demonstrated in 2010 [Argenti et al. 2013, Phys. Rev. A 87 053405].
  • The user friendly setup of the package was tested
  • The benchmarking of neon- and argon photoionization, and especially the issue of how to obtain a correct energy position of the so-called Cooper minima in argon was discussed.