Soft parameters in Coulomb potential of noble atoms for nonsequential double ionization: Classical ensemble model and simulations

We propose a procedure based on the classical ensemble model to determine the soft parameter in the Coulomb potential of noble atoms, the important parameters used in the simulations of nonsequential double ionizations (NSDI). These parameters are determined based on two conditions: ensuring the positive kinetic energy of two electrons and preventing the atom from autoionization. The optimal values of the soft parameters for He, Ne, Ar, Kr, and Xe atoms are around 0.85, 1.1, 1.5, 1.8, and 2.0 a.u., respectively. The classically allowed initial position of electrons is analytically derived from soft parameters. A simulation of NSDI using 2,000,000 particles has been done using the obtained parameters to achieve the probability distribution of the single and double ionizations. The procedure is comprehensively illustrated for Ar and He atoms and the result in this study is validated by comparing the ratio of double to single ionization yield and correlated two-electron momentum distributions with that in recent experiments. (c) 2022 Elsevier B.V. All rights reserved.