Atomic MP2 correlation energies fast and accurately calculated by FEM extrapolations

A p -version FEM-MP2 (finite element Møller-Plesset second order perturbation) program for accurate MP2 correlation energies of closed shell atoms has been further improved: by radial transformations , inclusion of global radial factors of the form with a sloping function and discretization in x rather than r . Adding logarithmic extrapolations to a sequence , of MP2 energies obtained from low order (linear) finite-element calculations resulted in a very fast high precision approach to MP2 correlation energies. The accuracy gain over the directly calculated values is around five orders for He bare nucleus, He-HF and Be-HF, four orders for Ne-HF almost tripling the number of significant digits. Maximal effective numbers of 16 to 18 radial points were sufficient. A coupling between the maximal l -value (here ) and a suitable maximal number of radial points is observed amounting to about .