Becke, Lee, Yang, and Parr

In addition to conventional ab initio methods, techniques based on the density functional theory (DFT) have also been used to study the Diels-Alder reaction between butadiene and ethylene97-99. With these kinds of methods, a concerted mechanism through a symmetric transition state is also predicted. Several kinds of density functionals have been used. The simplest one is based on the Local Density Approach (LDA), in which all the potentials depend only on the density. More sophisticated functionals include a dependence on the gradient of the density, such as that of Becke, Lee, Yang and Parr (BLYP). 

The gradient-corrected Becke, Lee, Yang, and Parr (BLYP) [30,31] exchange correlation functional has been shown to give a good description of aqueous systems [32-34] it was employed in our present simulation. 

Pure DFT methods are defined by pairing an exchange functional with a correlation functional. For example, the well-known BLYP functional pairs Becke s gradient-corrected exchange functional with the gradient-corrected correlation functional of Lee, Yang and Parr. 

B3LYP Becke s three-parameter exchange functionals and Lee, Yang, and Parr s correlation functionals... 

In the majority of current theoretical pubhcahons deahng with organocatalysis, Becke s [8a, b] three parameter hybrid functional B3 and the Lee, Yang, and Parr (LYP) correlahon functional [8c] are used in combinahon with standard split valence basis sets (e.g., 6-3IG). In most cases, polarization functions that allow a greater flexibiHty of angle are added (for example, [d,p] means addihonal d-functions for second-row atoms, and additional p-funchons for hydrogen atoms)... 

No theoretical studies were reported in the previous volume <1996CHEC-11(7)89> for these 5-5 bicyclic systems. Since then a number of computational studies have been carried out. The structure and properties of cyclic sulfites 3a and 3b and thionosulfites 3c and 3d have been reported <2003HAC587, 2005HCA1451>. Density functional theoretical (DFT) calculations using the Becke s exchange with Lee, Yang, and Parr correlation functional (B3LYP/6-31G level) have shown that the cyclic sulfite 3b is more stable than its diastereomer 3a. 

Typically in the literature, a complete specification of the exchange and correlation functionals is accomplished by concatenating the two acronyms in that order. Thus, for instance, a BLYP calculation combines Becke s GGA exchange with the GGA correlation functional of Lee, Yang, and Parr. 

Becke s 3-parameter fit using the correlation functional by Lee, Yang and Parr... 

Becke s three-parameter hybrid functional using the Lee, Yang and Parr correlation functional... 

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