BLYP correlation

BLYP correlation functional C Lee, W Yang, RG Parr. Phys Rev 837 785-789,... 

BLYP Becke correlation functional with Lee, Yang, Parr exchange Gradient-corrected... 

The DFT and MP2 calculations produce very similar structures, although the BLYP bond length is again longer than those of the other functionals. Hartree-Fock theory predicts a bond length which is significantly shorter than the methods including electron correlation. 

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. 

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