FULL SPIN-ORBIT CORE-VALENCE CONFIGURATION INTERACTION STUDIES OF $Cs_{2}$, $Cs_{2}^{+}$, LiBe, AND LiMg.

$^{1}$ W. C. Ermler, R. B. Ross and P.A. Christiansen, Adv. Quantum Chem. 19 , 139 (1988). Department of Chemistry Chemical Engineering, Stevens Institute of Technology Hoboken, NJ.07030. $^{2}$ R. M. Pitzer and N. W. Winter, J. Phys. Chem, 92 , 3061 (1988).Author Institution: Molecular Science Research Centre, Pacific Northwest Laboratory; Department of Chemistry, Clarkson UniversityAn accurate ab intio method for the treatment of molecules and clusters as few-electron systems has been developed. The procedure is based on the theory of relativistic effective core potentials (REP) and one- and two-electron core-valence polarization potentials (CVPP). REPs are derived using ab intio numerical Dirac-Fock atomic wavefunctions and shape consistent pseudo-spinors, while CVPPs are obtained using the adiabatic field method in the context of $\omega-\omega$ coupled molecular wave $functions.^{1}$ Valence electrons in molecules and clusters are addressed using a configuration interaction (CI) procedure that incorporates spinorbit operators extracted from the respective $REPs.^{2}$ The REPs and CVPPs are incorporated in full-spin-orbit-CI calculations on $Cs_{2}^{+}$, $Cs_{2}$, LiBe, and LiMg. Spectroscopic constants and electronic spectra of both valence and Rydberg states are in excellent agreement with recent experimental and all electron ab intio results