RMT: R-matrix with time-dependence. Solving the semi-relativistic, time-dependent Schrodinger equation for general, multielectron atoms and molecules in intense, ultrashort, arbitrarily polarized laser pulses
Abstract
RMT is a programme which solves the time-dependent Schrodinger equation for general, multielectron atoms, ions and molecules interacting with laser light. As such it can be used to model ionization (single-photon, multiphoton and strong-field), recollision (high-harmonic generation, strong-field rescattering) and, more generally, absorption or scattering processes with a full account of the multielectron correlation effects in a time-dependent manner.
Calculations can be performed for targets interacting with ultrashort, intense laser pulses of long wavelength and arbitrary polarization. Calculations for atoms can optionally include the Breit-Pauli correction terms for the description of relativistic (in particular, spin-orbit) effects.
Program summary Program Title: (RMT) R-matrix with time-dependence Program Files doi: http://dx.doi.org/10.17632/3ptyfg2bmx.1 Licensing provisions: GPLv3 Programming language: Fortran Nature of problem: The interaction of laser light with matter can be modelled with the time-dependent Schrodinger equation (TDSE). The solution of the TDSE for general, multielectron atomic and molecular systems is computationally demanding, and has previously been limited either to particular laser wavelengths and intensities, or to simple, few-electron cases.
RMT overcomes this limitation by using a general approach to modelling dynamics in atoms and molecules which is applicable to multielectron systems and a wide range of perturbative and non-perturbative phenomena. solution method: We use the R-matrix paradigm, partitioning the interaction region into an 'inner' and an 'outer' region. In the inner region (within some small radius of the nucleus/nuclei), full account is taken of all multielectron interactions including electron exchange and correlation.
In the outer region, far from the nucleus/nuclei, these are neglected and a single, ionized electron moves in the long-range potential of the residual ionic system and the laser field. The key computational aspect of the RMT approach is the use of a different numerical scheme in each region, facilitating efficient parallelization without sacrificing accuracy.
Given an initial wavefunction and the electric field of the driving laser pulse, the wavefunction for all subsequent times and the associated observables are computed using an explicit, Arnoldi propagator method. Additional comments including restrictions and unusual features: The description of the atomic/molecular structure is provided from other, time-independent R-matrix codes [1], [2], [3], and the capabilities (in terms of structure) are, in some sense, inherited therefrom.
Thus, the atomic calculations can optionally include Breit-Pauli relativistic corrections to the Hamiltonian, in order to account for the spinorbit effect. However, no such capability exists for the molecular case.
Furthermore, the fixed-nuclei approximation is adopted in the molecular calculations (so nuclear motion is neglected). Similarly, all calculations are restricted to the description of a single electron in the outer region, and consequently the study of double-ionization phenomena is not yet within the capabilities of the method.
Finally, the parallel strategy employed necessitates the use of at least two (and usually many more) computer cores. As a result, there is no option for serial calculations and, for most realistic cases, a massively parallel architecture (several hundred cores) will be required.
Program repository available at: https://gitlab.com/Uk-amor/RMT References [1] C. P.
Ballance Parallel R-matrix codes, http://connorb.freeshell.org. [2] R-matrix II codes, http://gitlab.com/uk-amor/rmt/rmatrixii. [3] Z. Masin et al UKRmol+: a suite for modelling of electronic processes in molecules interacting with electrons, positrons and photons using the R-matrix method, Comput.
Phys. Commun., accepted, http: //dx.doi.org/10.1016/j.cpc.2019.107092. (c) 2019 Elsevier B.V.
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