DIMERS OF RARE-GAS ATOMS - CCSD(T), CCSDT AND FCI CALCULATIONS ON THE(HE)(2) DIMER, CCSD(T) AND CCSDT CALCULATIONS ON THE (NE)(2) DIMER, AND CCSD(T) ALL-ELECTRON AND PSEUDOPOTENTIAL CALCULATIONS ON THE DIMERSFROM (NE)(2) THROUGH (XE)(2)

Rare gas atom dimers from (He)(2) to (Xe)(2) were studied by beyond Ha rtree-Fock methods and the results obtained were compared with experim ental values. In the case of (He)(2), the CCSD(T), CCSDT, and FCI resu lts enable estimation of the role of triple and quadruple excitations. CCSD(T) already yields reliable stabilization energy values. Passing from CCSD(T) to CCSDT leads to only a small increase in the stabilizat ion energy; a very similar value was surprisingly obtained for the (Ne )(2) dimer. For the (Ne)(2) and (Ar)(2) dimers, the all-electron and t he effective core potential (ECP) results were compared. Correcting th e ECP CCSD(T) characteristics for (Kr)(2) and (Xe)(2) by the factors f ound for (Ne)(2) and (Ar)(2) resulted in very good agreement with the experimental values.