In this study, potential energy curves for the lowest-lying electronic states correlating with the first four dissociation channels were determined using the cc-pVQZ basis sets and CASSCF/MRCI wavefunctions. All valence orbitals plus one set of s and p correlation functions were included in the active space. A whole set of spectroscopic constants completes the characterization of each state. In its ground state (X(1)Sigma(+)), BeMg is weakly bound (D-e = 0.05 eV) and consequently, has a long internuclear equilibrium distance (R-e = 3.300 Angstrom, omega(e) = 44.2 cm(-1)). In previous theoretical works, the internuclear equilibrium distance was calculated to be around 4.5 Angstrom (SCF, CCD, and CEPA methods) and 5.1 Angstrom (QCID method). (C) 2003 Elsevier Science B.V. All rights reserved.