Many-electron correlated exponential wavefunctions. A quantum Monte Carlo application to H2 and He2+

We propose to expand the solution of the Schrِdinger equation for an atomic or molecular system as a linear combination of many-electron explicitly correlated exponentials. A series of trial wavefunctions has been optimized, minimizing the variance of the local energy for H2 and He2+ in their ground state at the equilibrium distance, and their variational energy has been computed using the variational Monte Carlo method. The He2+ wavefunctions have been used in a series of fixed node diffusion Monte Carlo simulations, showing that, using a small number of terms, one can obtain a good estimate of the exact energy.