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An algorithm to sample the exact (within the nodal error) ground state distribution to find nondifferential properties of multielectron systems is developed and applied to first-row atoms. Calculated properties are the distribution moments and the electronic density at the nucleus (expected value of the δ operator). For this purpose compact trial functions are developed and optimized, and a new estimator for the δ is formulated. A comparison is made with results of highly accurate post-Hartree-Fock calculations, thereby illuminating the nodal error in our estimates. In general, we obtain more accurate estimates for the distribution moments than those obtained previously using Monte Carlo methods, despite the relative crudeness of our trial functions. We confirm the literature values for the electron density at the nucleus for the lighter atoms (Li-C), but disagree with previous (Monte Carlo) estimates for the heavier ones (N-Ne).

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New density functionals are employed to represent the correlation and exchange energies (per electron) in the calculation of rare gas interactions from the electron gas model. The correlation energy density functional is a rational function involving two parameters which were optimized to reproduce the correlation energy of He atom. Our results indicate that these parameters are "universal", i.e., they are accurate for all rare gas atoms. The exchange energy density functional is that recommended by Handler. Rare gas systems Xl and XY are investigated. where X and Yare He. Ne, Ar. and Kr. The results are a significant improvement over those available from competing electron gas models.