The potential energy curves (PECs) of the ground states of YbX ( X = F, Cl, Br, I, At) are investigated using the unrestricted coupled cluster singles and doubles method with perturbative treatment of triple excitations. The relativistic effective core potentials basis sets and full electron Huzinaga's well tempered basis sets for Yb are used. The present spectroscopic constants calculated based on the PECs are in good agreement with the experimental data available at present. Isotopic effects on spectroscopic constants are also examined. (c) 2008 Elsevier B. V. All rights reserved.