Simple correlated wave functions for accurate electron densities: An application to neon

We carry out a systematic study of the stability of the electron density in the ground state of neon upon adding well-defined improvements in the corresponding configuration-interaction (CI) wave functions. We describe a precise manner of obtaining a CI wave function which yields the electron density with an error no larger than 0.5% for a wide range of values of r. An accurate analytical density is obtained thereby, and a comparison with the Hartree-Fock density is made. Contrary to common belief, we find rather large discrepancies at r>2 bohrs between our accurate density and those obtained from two other CI wave functions, which account for more than 85% of the correlation energy.