RMT: R-matrix with time-dependence. Solving the semi-relativistic, time-dependent Schrödinger equation for general, multielectron atoms and molecules in intense, ultrashort, arbitrarily polarized laser pulses

Abstract

RMT is a program which solves the time-dependent Schrödinger 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 SUMMARYProgram Title: (RMT) R-matrix with time-dependence Licensing provisions: GPLv3 Programming language: Fortran Program repository available at: https://gitlab.com/UK-AMOR/RMT Computers on which the program has been tested: Cray XC40 BESKOW, Cray XC30 ARCHER, Cray XK7 TITAN, TACC Stampede2, DELL linux cluster, DELL PC Number of processors used: Min. 2, Max. tested 16,416 Number of lines in program: 25,247 Distribution format: git repository Nature of problem:The interaction of laser light with matter can be modelled with the time-dependent Schrödinger equation (TDSE). The solution of the TDSE for general, multielectron atomic and molecular systems is computationally demanding, and has previously been limited to either 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 multi-electron 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 approach 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, timeindependent 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

UKRmol+: A suite for modelling electronic processes in molecules interacting with electrons, positrons and photons using the R-matrix method

“…Here we present some illustrative results of both scattering and photoionization calculations. For RMT results, we refer the reader to Brown et al [13].…”

“…The UKRmol+ suite is a completely reengineered and extended version of the UK polyatomic molecular R-matrix codes. The suite enables the calculation of low energy electron and positron (excluding positronium formation) scattering from molecules and molecular clusters, photoionization and also the production of input for the RMT suite of codes [13]. Use of the GBTOlib library (included in the releases but developed as a stand-alone entity) means that both GTOs and BTOs can be used to describe the unbound particle.…”

“…In practice, especially in the case of scattering calculations, the radius r = a typically does not lie in the asymptotic region. Therefore the R-matrix is first propagated [17,18,19] in the static multipole molecular potential, see Appendix A.2 in [13], to a large distance a p (typically 100 a 0 ) where the matching of the radial functions to known asymptotic expressions is performed [20,15].…”

“…The RMT (R-matrix with time) code [13] solves the time-dependent Schrödinger equation to describe molecules in intense, ultrashort, arbitrarilypolarized laser pulses. It requires the following data from UKRmol+:…”

“…• the list of outer region channels and coefficients for reconstruction of the long-range potentials that couple the channels (produced by SWIN-TERF; see Appendix A in [13] for a detailed description of these),…”