PERTURBATIVE VARIATIONAL APPROXIMATION OF THE GROUND-STATE OF 2-ELECTRON ATOMS

Here, we study the applicability of the perturbative variational metho d (PVM) to obtain the ground-state energy and wavefuncfion of the two- electron atoms. The convergence of the method has been studied with di fferent bases and we have checked whether it is faster if we work with an orthogonal or quasi-orthogonal basis. We have focused our attentio n on the polynomial basis and our best results are very close to the b est results provided for other calculations that include non-analytica l terms in the basis. However, we have to use a number of states in a basis ten times larger than that used in other calculations.