Spatial Correlation and Molecular Properties in Extended Hartree—Fock Calculations

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Abstract
Using the extended Hartree—Fock multiconfiguration wavefunctions of Das and Wahl, the first‐ and second‐order density matrices are derived for the ground states of H2, Li2, and F2. The method of Weinhold and Wilson is used to obtain the natural orbitals and natural geminals. Expectation values of the following one‐electron operators are calculated: (rai)−1, zai2, and rai2. Expectation values of the two‐electron confocal elliptic coordinate operator, (ξi—ξj)2, (ηi—ηj)2 and cos (φi—φj), together with the Cartesian coordinate operator (zai—zaj)2, are also calculated. The two‐electron expectation values provide a measure of in—out left—right, and angular correlation. The quadrupole moment and diamagnetic susceptibility of H2, Li2, and F2 are calculated as functions of R. Experimental values are lacking for Li2 and F2. Good agreement is obtained with experiments for H2 at its equilibrium separation.