Mpller-Plesset perturbation theory methodology

The accurate calculation of these molecular properties requires the use of ab initio methods, which have increased enormously in accuracy and efficiency in the last three decades. Ab initio methods have developed in two directions first, the level of approximation has become increasingly sophisticated and, hence, accurate. The earliest ab initio calculations used the Hartree-Fock/self-consistent field (HF/SCF) methodology, which is the simplest to implement. Subsequently, such methods as Mpller-Plesset perturbation theory, multi-configuration self-consistent field theory (MCSCF) and coupled-cluster (CC) theory have been developed and implemented. Relatively recently, density functional theory (DFT) has become the method of choice since it yields an accuracy much greater than that of HF/SCF while requiring relatively little additional computational effort. 

Two general groups of methodologies are used to solve the Schrodinger equation in combination with cluster models, the Hartree-Fock (HF) approach and related methods to include correlation effects like Mpller-Plesset perturbation theory (MP2) or configuration interaction (Cl) [58,59] and the Density Functional Theory (DFT) approach [59,60]. 

An in-depth description of the theoretical basis of these methodologies as well as other computational techniques can be found in Refs. [5,8]. The dynamic correlation energy can be efficiently recovered by using the Cl (configurational interaction), Mpller-Plesset perturbation theory (MP ), and coupled cluster (CC) methods, whereas multireference Cl methods such as complete active space self-consistent field (CASSCF) allow an adequate description of the static correlations. 

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