Coupled Electron-pair Approach

Parallel to these endeavors, work started in Germany on new concepts to account for electron correlation. The independent electron pair approach (lEPA) was developed by Ahlrichs and Kutzelnigg, followed a few years later by the CEPA (coupled electron pair approach).The relation of these methods to contemporary Moller-Plesset second order (MP2) and coupled cluster treatments is discussed in Ref. 60. Work on circular dichroism by Ruch and on the chemical shift by Voitlander showed the variety of ab initio problems treated. The special priority program of the DFG from 1966-1970 demonstrated the intended impact. 

CEPA Coupled electron pair approach N Slight underestimate of bonding... 

Neese, R, Wennmohs, E, and Hansen, A. (2009). Efficient and accurate local approximations to coupled-electron pair approaches An attempt to revive the pair natural orbital method, / Chem. Phys. 130, p. 114108, doi 10.1063/l.3086717. 

IIL THEORY OF PAIR APPROACHES A. The Ori nal Coupled Electron-pair Approach... 

Gabriel et al. [60] reported ab initio coupled electron pair approach (CEPA) DMSs of SiH2 for X Ai and states represented with polynomials. Absorption intensities T = 300 K) were computed and plotted. 

In Section 5.2 we consider how to go beyond the lEPA by incorporating coupling between different pairs of electrons. We will discuss the coupled pair many-electron theory (CPMET) which is also called the coupled-cluster approximation (CCA). We then describe a number of simplifications to this rather sophisticated approach in particular, we consider the coupled electron pair approximation (CEPA). Finally, in Subsection 5.2.4 we present some numerical applications of coupled-pair theories. 

Another interesting application of the total energy approach involves superconductivity. For conventional superconductors, the 1957 theory of Bardeen, Cooper and Schrieffer [26] has been subject to extensive tests and has emerged as one of the most successful theories in physics. However, because the superconducting transition temperature Tc depends exponentially on the electron-phonon coupling parameter X and the electron-electron Coulomb parameter p, it has been difficult to predict new superconductors. The sensitivity is further enhanced because the net attractive electron-electron pairing interaction is proportional to X-p, so when these parameters are comparable, they need to be determined with precision. 

---