SDTQ-MBPT

This same quantity was calculated also using a coupled-cluster method, which includes single and double excitations, and a triple-excitation correction, the so-called CCSD-T technique. The results were found to be quire similar to the MP4 values for each basis set examined. The authors suggest that because of the small contributions from infinite summations, SDTQ-MBPT(4) is much more cost effective than is CCSD-T. 

MP4 Moller-Plesset variant of fourth order (—>) MBPT. There are different flavors of this model, depending on the level of excitations explicitly admitted (SDQ, SDTQ). 

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