Exchange correlation Becke

Professor Axel Becke of Queens University, Belfast has been very actively involved in developing and improving exchange-correlation energy functionals. For a good recent overview, see ... 

Becke A D 1995 Exchange-correlation approximations in density-functional theory Modern Eiectronic Structure Theory vol 2, ed D R Yarkony (Singapore World Scientific) pp 1022-46... 

L. iitortunately, this simple approach does not work well, but Becke has proposed a strategy which does seem to have much promise [Becke 1993a, b]. In his approach the exchange-correlation energy Exc is written in the following form ... 

B3P86 Becke exchange, Perdew correlation Hybrid... 

Becke, A. D., 1995, Exchange-Correlation Approximations in Density-Functional Theory in Modem Electronic Structure Theory, Part II, Yarkony, D. R., World Scientific, Singapore. 

Becke, A. D., 1996b, Current-Density Dependent Exchange-Correlation Functionals , Can. J. Chem., 74, 995. 

Proynov, E., Chermette, H., Salahub, D. R., 2000, New T-Dependent Correlation Functional Combined with a Modified Becke Exchange , J. Chem. Phys., 113, 10013. 

All electron calculations were carried out with the DFT program suite Turbomole (152,153). The clusters were treated as open-shell systems in the unrestricted Kohn-Sham framework. For the calculations we used the Becke-Perdew exchange-correlation functional dubbed BP86 (154,155) and the hybrid B3LYP functional (156,157). For BP86 we invoked the resolution-of-the-iden-tity (RI) approximation as implemented in Turbomole. For all atoms included in our models we employed Ahlrichs valence triple-C TZVP basis set with polarization functions on all atoms (158). If not noted otherwise, initial guess orbitals were obtained by extended Hiickel theory. Local spin analyses were performed with our local Turbomole version, where either Lowdin (131) or Mulliken (132) pseudo-projection operators were employed. Broken-symmetry determinants were obtained with our restrained optimization tool (136). Pictures of molecular structures were created with Pymol (159). 

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