Charge transfer in C4+ +H,H2 collisions. A comparison of ab initio and model potential methods L.F. Errea (1), J.D. Gorfinkiel (1), C. Harel (2), H. Jouin (2), A. Macias (1), L. Mendez (1), B. Pons (2) and A. Riera (1) (1) Departamento de Quimica C-XIV, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid, Spain (2) Centre Lasers Intenses et Applications, Universite de Bordeaux-I, 351 Cours de la Liberation, 33405 Talence, France We have calculated charge transfer cross sections in C4+ collisions with H and H2. We employed an effective potential to describe C4+ core and checked the validity of this technique by explicit comparison with ab initio resuls. The H2 molecule has been described using a one-center model potential. We propose to use the equivalent electrons interpretation in an alternative way by building two-electron basis functions as products of diabatic one-electron ones. This technique permits to extend the range of validity of the model potential.