Ab initio calculations on the potential energy curves and electronic structures of the ground and low-lying electronic states for the mixed transition metal dimer CrCu have been carried out by using the internally contracted multireference singles and doubles configuration interaction method MRCI(SD) + Q. The spectroscopic constants of the selected electronic states were obtained. The results are presented supporting the (6)Sigma(+) ground state, by contrast to the assigned ground state (4)Sigma in ESR of CrCu. The electronic structures of the ground state and the low-lying states are multireference in character, and the ground state (6)Sigma(+) is mainly dominated by strong intra-atomic d-d exchange interactions on the atom Cr. (c) 2006 Elsevier B.V. All rights reserved.