Natural Orbitals for H2

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Abstract
Natural‐orbital (norb) expansion coefficients are presented for the LCAO–MO–SCF–CI wavefunction of Fraga and Ransil for separations between 1.0 and 12.0 bohrs. These results are compared in detail with those obtained by Shull and Prosser for the He2++ system. Judged at the two‐norb level, the norb expansion converges faster for He2++ than for H2 at all internuclear separations. Otherwise, the norb coefficients for the two systems have quite similar dependence on scaled separations. The occurrence of more than one positive norb coefficient is found to be an intrinsic property of the approximate wavefunction.