Theoretical studies of selected diatomic and triatomic molecules containing copper and the simple metals Li, Na, K, Be, and Al are presented, with emphasis on elucidating the nature of the bonding in mixed transition metalndash;simple metal systems. Large Gaussian basis sets are used in the diatomic calculations, and are used to calibrate the triatomic calculations, in which somewhat smaller Gaussian basis are employed. Electron correlation is incorporated using both the singlehyphen;reference singles plus doubles configuration interaction and coupled pair functional methods. We find that alkali atoms form very polar sgr; bonds with copper, and that the ionicity increases with the inclusion of higher excitations, because they improve the electron affinity of copper, which in turn allows a larger negative charge on copper. Aluminum is found to form stronger bonds than beryllium, since it does not have to undergosphybridization. Some of the trimers bond by forming threehyphen;center threehyphen;electron bonds. These multicenter bonds are quite strong even when compared to the twohyphen;electron bonds in the dimers or to other bonding mechanisms in the trimers.
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