Cusp values and electron densities at coalescence

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Abstract
The correlation between errors in (a) calculated cusp values and (b) calculated electron densities at coalescence are examined for the electron-nucleus and electron-electron pairs in helium. Calculations for 25 fully optimized variational wavefunctions for the ground state are presented. Although a wide variety of functional forms are represented in the set of wavefunctions studied, a strong correlation between (a) and (b) is obtained in the case of the electron-nucleus pair, and a weaker but still significant correlation is found for the electron-electron pair.