FIG. . Le : Energy convergence of the ground state of Cr 2 with respect to the number of determinants N det in the reference space. e zeroth-order energy E (0) (do ed) , its second-order corrected value E (0) + E (dashed) as well as its renormalized version E (0) + ZE (solid) are represented. Right: Zeroth-order energy E (0) as a function of the second-order energy E (do ed lines) or its renormalization variant Z E (solid lines). A linear t (dashed lines) of the last 2 points is also reported for comparison. See Table for raw data.