Explicitly correlated Helium wave function and hyperspherical coordinates

Abstract: Wave functions of a new functional kind have been proposed for Helium-like atoms in this work . These functions explicitly depend on interelectronic and hyperspherical coordinates. The best ground state energy for the Helium atom $ -2.903724376677 a.u.$ has been calculated with variational method with basis set of simple functions with a single exponential parameter. To the author's knowledge, this is the best result with use of hyperspherical coordinates so far. Comparable result has been obtained for the hydrogen anion. For Helium atom, our best wave functions matched the Kato cusp conditions within the accuracy below $6.10^{-4} $. An important feature of proposed wave functions is the inclusion of negative powers of $R=\sqrt(r^{2}{1}+r^{2}{2})$ in combination with positive powers of $r_{12}$ into the wave function. We showed that this is necessary condition for proposed wave function to be a formal solution of Schr\"odinger equation.