Relationship of correlation energy and size

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AbstractAnalysis of available data on atoms has led to a relatively simple empirical relationship between the correlation energy and second moment <r2>, a measure of the size of the electron density. With the aid of this simple relationship it is possible to predict correlation energies with fair accuracy given the SCF or Hartree–Fock limit values for the size of the electron density. Preliminary extensions of this work to two‐ and ten‐electron molecules indicate that it may be possible to predict molecular correlation energies to semiquantitative accuracy from SCF data on the electronic distribution.