The performance of the recently introduced
2 method 
is investigated for some diatomic molecules.
For this end, ground state energies are calculated at the MP4 level
for various basis sets of
increasing size. With negligible extra effort, the
2, F4, and [2/2] estimators
are obtained, together with information on the reliability of the
series . The results are compared to more expensive CCSD(T) results. Also,
electronic energy hypersurfaces are calculated at these levels.
As a further possibility to test the performance of the method, vibrational frequencies
and other spectroscopic constants of diatomic molecules are calculated by fitting
different analytic functions to the hypersurfaces obtained by different
methods and compared to experimental data.
 H. H. H. Homeier, Correlation energy estimators based on Møller-Plesset
theory, J. Mol. Struct. (Theochem), 366:161-171, 1996.
Category: Ab initio
Keywords: Correlation energy, Perturbation theory, Morse potential,
Anharmonicity constant, Hypersurface, Spectroscopic constants