Full CI calibration of model hamiltonian,large basis set studies of the H2-H2 van der Waals interaction.

The non-variational CEPA2 PNO ansatz, recently employed in detailed studies of the H₂-H₂ van der Waals interaction by Burton and Senff and the full CI extrapolation studies on the same system by Burton are discussed in relation to the explicit full CI study of Harrison and Handy for the planar T configuration of H₂-H₂ (R = 6.5 a_o) in a basis of 80 functions.