Zero-differential-overlap molecular orbital theory

We shall not discuss at length further simplifications, known as next-neighbors interactions (for core integrals), zero-differential-overlap (for two-electron repulsion integrals) etc., which were introduced into the formalism of the n molecular orbital theory after the basic work of Goeppert-Mayer and Sklar. Detailed reviews on these topics have been published 38,39,40,41,42). Let us just show why zero-differential-overlap can be justified in terms of orthogonalized orbitals 43,22,44). 

By ab initio we refer to quantum chemical methods in which all the integrals of the theory, be it variational or perturbative, are exactly evaluated. The level of theory then refers to the type of theory employed. Common levels of theory would include Hartree-Fock, or molecular orbital theory, configuration interaction (Cl) theory, perturbation theory (PT), coupled-cluster theory (CC, or coupled-perturbed many-electron theory, CPMET), etc. - We will use the word model to designate approximations to the Hamiltonian. For example, the zero differential overlap models can be applied at any level of theory. The distinction between semiempirical and ab initio quantum chemistry is often not clean. Basis sets, for example, are empirical in nature, as are effective core potentials. The search for basis set parameters is not usually considered to render a model empirical, whereas the search for parameters in effective core potentials is so considered. 

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