Couple cluster technique, intermolecular

In this substection we will shortly discuss the computational methods used for calculation of the spin-spin coupling constants. Two main approaches available are ab initio theory from Hartree-Fock (or self-consistent field SCF) technique to its correlated extensions, and density function theory (DFT), where the electron density, instead of the wave function, is the fundamental quantity. The discussion here is limited to the methods actually used for calculation of the intermolecular spin-spin coupling constants, i. e. multiconfigurational self consistent field (MCSCF) theory, coupled cluster (CC) theory and density functional theory (DFT). For example, the second order polarization propagator method (SOPPA) approach is not... 

Energy is an extensive property. This fundamental thermodynamic principle is introduced early in most general chemistry textbooks, and it provides the foundation for the supermolecule description of intermolecular interactions. Unfortunately, not all electronic structure techniques are size con-sistent (or more generally size extensive ). That is, the energy computed by some methods does not scale properly with the number of noninteracting fragments. Readers interested in more detail may be interested in the sections discussing size consistency and extensivity in the review of coupled-cluster theory by Crawford and Schaefer. ... 

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