Refined universal potentials in atomic collisions

Abstract

Recent precision experiments as well as individual pair-potential calculations (ab-initio or free-electron-gas for overlapping HFS atoms) revealed significant deviations from frequently used standard potentials, such as e.g., Thomas-Fermi or Molière potentials. Some of the individual features result from atomic shell structures or finite size of the Seitz-Wigner cells (of solid-state target atoms), and are definitely beyond the scope of any "universal" description. However, the more gradual changes of shape and magnitude of the repulsive part of the pair potentials in dependence of Z1 and Z2 may well be assessed by applying free electron statistics for homo-nuclear cases and using appropriate combination rules for hetero-nuclear cases. The free electron model is extended beyond Firsov's treatment by including additional terms for exchange and correlation energy. The final parameters are obtained in a semi-empirical way from overlapping Hartree-Fock-Slater atoms rather than Thomas-Fermi atoms. Thus, a precision was achieved which appears quite sufficient for most present atomic collision problems. © 1982.