A combined B-spline R-matrix approach for the study of time-dependent multielectron dynamics in complex atoms.

Experiments with ultrafast lasers are becoming increasingly focused on the role of multi\-electron effects~[1] and the capabilities of mid-IR lasers~[2], both of which present considerable challenges to current computational methods. A successful time-dependent multi\-electron approach, therefore, requires two things: a compact, accurate atomic-structure description, and an efficient time-propagation scheme. Given their individual desirable characteristics and common $B$-spline basis, the time-independent $B$-spline atomic \hbox{$R$-matrix} code (BSR)~[3] and the $R$-matrix with time-dependence method (RMT)~[4] are natural choices to provide, respectively, the atomic-structure description and propagation scheme for probing time-dependent behaviors in general atomic systems. We present our efforts in combining the two approaches, which we hope will enable the investigation of phenomena such as auto-ionization and spin-orbit dynamics~[5] in multi\-electron systems. [1] T.~Mazza et al., Nat.\ Commun.~{\bf 6} (2015) 6799. [2] T.~Gaumnitz et al., Opt.\ Express~{\bf 25} (2017) 27506. [3] O.~Zatsarinny, Comput.\ Phys.\ Comm.~{\bf 174} (2006) 143. [4] A.~C. Brown et al., Comput.\ Phys.\ Comm.~(2019) 107062. [5] J.~Wragg et al., Phys.\ Rev.\ Lett.~{\bf 123} (2019) 163001.