Electron correlation method Density-functional theory Mpller-Plesset

Considering these two drawbacks, the use of Density Functional Theory (DFT) within its Kohn-Sham (KS) formulation is very appealing First, because the cost of a KS-DFT calculation is at most of the same order of magnitude as a Hartree-Fock one, whereas most of the description of electron correlation is taken into account, it is substantially less expensive than traditional correlated techniques. Moreover, most order n methods which are presently under development are all built on the DFT framework. Indeed, in a number of systematic validation studies , DFT has been shown successfully predicting various molecular properties, often giving results of quality comparable to or better than second order Mpller-Plesset (MP2) perturbation theory. It appears more and more evident that the use of DFT techniques could lead to reliable theoretical evaluation of ionization potentials. Moreover, the obtention of new exchange-correlation (XC) functionals is still under development, and one can expect that ionization potentials will be calculated more accurately in a close future. 

Basis Sets Correlation Consistent Sets Configuration Interaction Coupled-cluster Theory Density Functional Applications Density Functional Theory Applications to Transition Metal Problems G2 Theory Integrals of Electron Repulsion Integrals Overlap Linear Scaling Methods for Electronic Structure Calculations Localized MO SCF Methods Mpller-Plesset Perturbation Theory Monte Carlo Quantum Methods for Electronic Structure Numerical Hartree-Fock Methods for Molecules Pseudospectral Methods in Ab Initio Quantum Chemistry Self-consistent Reaction Field Methods Symmetry in Hartree-Fock Theory. 

In ab initio methods the HER approximation is used for build-up of initial estimate for and which have to be further improved by methods of configurational interaction in the complete active space (CAS) [39], or by Mpller-Plesset perturbation theory (MPn) of order n, or by the coupled clusters [40,41] methods. In fact, any reasonable result within the ab initio QC requires at least minimal involvement of electron correlation. All the technical tricks invented to go beyond the HFR calculation scheme in terms of different forms of the trial wave function or various perturbative procedures represent in fact attempts to estimate somehow the second term of Eq. (5) - the cumulant % of the two-particle density matrix. 

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