ENHANCEMENT FACTORS FOR ELECTRONS IN SOLIDS FOR SOME SIMPLE CASES |

H. Stachowiak, E. Boroński and G. BanachW. Trzebiatowski Institute for Low Temperature and Structure Research Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroc³aw 2, Poland |

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The approach to e^{+}-e^{-}
interaction in hellium proposed by Gondzik and Stachowiak proved to be
simple numerically and leading to reasonable results. This is why it
seemed to be particularly suited for generalizations to real solids, a
problem that in spite of more than thirty years of research in this
direction did not get yet a satisfactory solution. An obstacle up to
now was the necessity to solve integro-differential equations in two
dimensions. After overcoming this difficulty we were able to compute e^{+}-e^{-}
enhancement for core and valence electrons in lithium and for core
electrons in other two-electron core elements. Properties of the
electronic cloud screening the positron are investigated for different
coordinates of this particle. The results are compared to such
simplifying guesses concerning this problem as the local density, the
generalized gradient and the weighted density approximations. |

DOI: 10.12693/APhysPolA.99.503 PACS numbers: 71.60.+z, 78.70.Bj |