njit-etd2003-111 - New Jersey Institute of Technology

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exchange-correlation term is, itself, also divided into separate exchange and correlation
components in most actual DFT functions). A variety of functionals have been defined,
generally distinguished by the way that they treat exchange and correlation components. 19
• Local exchange and correlation functionals involve only the values of the electron
spin densities.
• Gradient-corrected functionals involve both the values of electron spin densities
and their gradients. 5uch functionals are also referred to as non-local in literature.
A popular gradient-corrected exchange functional is one proposed by Becke 2
; a
widely used gradient-corrected correlation functional is the LYP functional of
Lee, Yang and Parr. The combination of the two forms the B-LYP method.
B3LYP is Becke-style 3-parameter density functional theory (using the Lee-
Yang-Parr correlation functional).
2.3 Kinetics
2.3.1 Lindemann-Hinshelwood Mechanism for Unimolecular Reactions
A general theory for thermal unimolecular reactions that forms the basis for the current
theory of thermal unimolecular rates was proposed by Lindemann 21 in 1922. He proposed
that molecules become energized by bimolecular collisions, with a time lag between the
moment of collisional energy transfer and the time the molecule decomposes. Energized
molecules could then undergo deactivating collisions before decomposition occurred.
5teinfeld et al. 22 indicated that "A major achievement of Lindemann's theory is its ability
to explain the experimental finding that the reaction rate changes from first to second
order in going from the high- to low-pressure limit."