Monte Carlo variational study of Be: A survey of correlated wave functions

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Abstract
Using the Metropolis Monte Carlo integration technique, we calculate upper bounds to the correlation energy of a Be atom for a variety of wave functions. With this method, it is simple to treat unconventional wave functions, including those which depend on the interelectronic distance rij. We obtain about 40% of the correlation energy by using only a simple two‐parameter Jastrow function of rij with a single Slater determinant of Hartree–Fock orbitals. A four configuration wave function with this Jastrow function yields 87% of the correlation energy. Several wave functions derived from nonvariational methods are shown to give no correlation energy when used in a strictly variational computation.