For example, the following dataset,
TITLE Formaldehyde 631g* basis MP2 energy SYMMETRY CNV 2 END VARIABLES RCO 1.21597 A RCH 1.101978 A HCO -121.827934 D END BASIS 631G* ATOMS XAXIS -1 1.0 0.0 0.0 CARBON 6.0 0.0 0.0 0.0 OXYGEN 8.0 0.0 0.0 RCO H1 1.0 PTC CARBON OXYGEN XAXIS RCH HCO END MP2 ENERGY START FINISHsets up the geometry of H2CO using internal coordinates (see section 1.4), with a 631G* basis set.
MP2 calculates the 2nd order Møller-Plesset energy.
MP3 would calculate the 2nd and 3rd order energies.
MP4 would calculate the 2nd, 3rd and 4th order energies.
MP4SDQ results in a simplified MP4 calculation omitting the effects of the triple excitations.
If an MP4 calculation on H2CO is carried out with the above basis set and geometry then the output will contain the results of the SCF calculation, and then the following
MP2 CORRELATION ENERGY -0.3106004871 TOTAL MP2 ENERGY -114.1749063611 MP3 CORRELATION ENERGY -0.0050632476 TOTAL MP3 ENERGY -114.1799696087 MP4(SDQ) CORRELATION ENERGY -0.0085727121 TOTAL MP4(SDQ) ENERGY -114.1885423208 MP4 CORRELATION ENERGY -0.0189456598 TOTAL MP4 ENERGY -114.1989152685 Feenburg MP4 Energy -114.1998700402For each level the correlation energy is given, as well as the total energy i.e. the sum of all terms up to that point including the SCF energy. For MP2 or MP3 calculations the results given are a subset of those above. The Feenburg MP4 energy is a particular extrapolation of the Møller-Plesset series, see Chem. Phys. Lett. 211, 272 (1993).