B-Spline Atomic R-Matrix Calculations on the AMPGateway*

The B-spline R-matrix (BSR) approach [1], developed by the late Oleg Zatsarinny, is an alternative formulation of the well-known R-matrix method developed in Belfast under the leadership of Philip Burke [2]. The program computes transition-matrix elements for electron collisions with many-electron atoms and ions as well as photoionization processes at varying levels of sophistication. From these, cross sections and other observable quantities can be obtained. Atomic structure information can also be generated with BSR through energy levels and oscillator strengths. 

Improvements over the original incarnation of the R-matrix method include: 1) a B-spline basis for the radial functions, thus enhancing the range and accuracy of the original R-matrix method, and 2) a set of non-orthogonal bound and continuum orbitals enabling high accuracy to be achieved with compact configuration expansions. These improvements allow BSR to describe complex systems, e.g., electron scattering from heavy noble gases. The BSR code has also been adapted to study time-dependent electron dynamics such as attosecond photoionization delays and extended to treat fully-relativistic coupling schemes. See [3] for a comprehensive overview of the BSR method and its applications.

The BSR code has recently become available on the AMPGateway [4,5], an online portal containing some of the world's foremost atomic and molecular physics applications. The AMPGateway enables users to carry out full-scale BSR calculations without having to install the source code or apply for the computing resources necessary to carry out large calculations. I will briefly demonstrate how to carry out BSR calculations via the AMPGateway interface.

[1] O. Zatsarinny, Comp. Phys. Commun. 174, 273 (2006)

[2] P. G. Burke, "R-Matrix Theory of Atomic Collisions", Springer Series on Atomic, Optical, and Plasma Physics, Vol. 61 (Springer-Verlag, 2011)

[3] O. Zatsarinny and K. Bartschat, J. Phys. B 46, 112001 (2013)

[4] https://ampgateway.org/

 

[5] B. I. Schneider et al. PEARC ’20: Practice and Experience in Advanced Research Computing (2020) 270