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Functionals: Generalized Gradient Approximation
Different versions of the
Generalized Gradient Approximation (GGA) are discussed in the following articles:
 PW91:
Atoms, molecules, solids, and surfaces:
Applications of the generalized gradient approximation for exchange and correlation
J. P. Perdew, J. A. Chevary, S. H. Vosko, K. A. Jackson, M. R. Pederson, D. J. Singh, and C. Fiolhais
Phys. Rev. B 46, 6671 (1992) (subscription needed).
PW91 has as an ingredient the LDA correlation and a choice need to be made between VWN, PZ, and PW.
 PBE:
Generalized Gradient Approximation Made Simple
J. P. Perdew, K. Burke, and M. Ernzerhof
Phys. Rev. Lett. 77, 3865 (1996) (subscription needed).
PBE has as an ingredient the LDA correlation and a choice need to be made between VWN, PZ, and PW.
 BLYP:
Exchange: Densityfunctional exchangeenergy approximation with correct asymptotic behavior
A. D. Becke
Phys. Rev. A 38, 3098 (1988) (subscription needed).
Correlation: Development of the ColleSalvetti correlationenergy formula into a functional of the electron density
C. Lee, W. Yang, and R. G. Parr
Phys. Rev. B 37, 785 (1988) (subscription needed).
