Deng, Jia; Gill, Peter M. W.
We describe a hierarchy of approximations (MP2[x]) that allow one to estimate second-order Møller-Plesset (MP2) energies in a large basis set from small-basis calculations. The most cost-effective approximation, MP2[K], is significantly cheaper than full MP2 but numerical tests on small atoms and molecules indicate that it is nonetheless accurate. We conclude that MP2[K] is an attractive level of theory for large systems.
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