Generalized gradient approximations exchange correlation functionals

A variety of modern (meta-)GGA (generalized gradient approximation) exchange-correlation (xc) energy functionals, such as the van Voorhis Scuseria functional, are evaluated. For reliable property calculations, improved xc potentials with correct asymptotic behavior, such as SAOP" and GRAC," have been developed. 

The wave functions are expended in a plane wave basis set, and the effective potential of ions is described by ultrasoft pseudo potential. The generalized gradient approximation (GGA)-PW91, and local gradient-corrected exchange-correlation functional (LDA)-CAPZ are used for the exchange-correlation functional. 

Three types of exchange/correlation functionals are presently in use (i) functionals based on the local spin density approximation, (ii) functionals based on the generalized gradient approximation, and (iii) functionals which employ the exact Hartree-Fock exchange as a component. The first of these are referred to as local density models, while the second two are collectively referred to as non-local models or alternatively as gradient-corrected models. 

Gritsenko, O. V., Schipper, P. R. T., Baerends, E. J., 1997, Exchange and Correlation Energy in Density Functional Theory. Comparison of Accurate DFT Quantities With Traditional Hartree-Fock Based Ones and Generalized Gradient Approximations for the Molecules Li2, N2, F2 , J. Chem. Phys., 107, 5007. 

Local exchange-correlation functionals such as generalized gradient approximations (GGA) are continuum approximations, which can, at best, average over the discontinuity. In regions where the HOMO and LUMO are significant, they provide an approximate average description [39—41] ... 

The density functional calculations were performed using the Vienna Ab Initio Simulation Package (VASP). ° The spin-polarized generalized gradient approximation, Perdue—Wang exchange correlation function, and ultrasoft pseudopotentials were used. ... 

We use generalized gradient approximations (GGA) to the exchange-correlation (XC) functional of DFT for all NMR calculations that are reported here. All current dependent terms (28) in the XC functional are neglected. The M(CO)6 and [MO4]2-, M = Cr, Mo, W, calculations (7) employed the BP86 functional (29,30). All other calculations were performed with the PW91 GGA (57). 

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