Exchange-delocalization component

For simplicity numerous terms defined in Symmetry Adapted Perturbation Theory (SAPT) [17,18] higher order induction, exchange-induction and coupled HP response [19] or exchange-deformation [20] contributions are col-lectively defined here as delocalization component. ... 

For a better understanding of the nature of the adsorption forces between TNB and the siloxane surface of clay minerals, the decomposition scheme of Sokalski et al. [199] was applied. The results of such energy decomposition are presented in Table 6. They are in complete agreement with qualitative conclusions presented above. One may see that two dominant attractive contributions govern the adsorption of TNB. As it is expected, one is an electrostatic contribution, and the other one is contribution, which includes components that originate from the electronic correlation. The electronic correlation related contributions include the dispersion component and a correlation correction to electrostatic, exchange, and delocalization terms of the interaction energy. 

One can see that the delocalization and exchange components are mainly responsible for the strength of the analyzed dihydrogen bonds since these terms correlate with the H H distance. These terms increase (their absolute values) with a decrease in intermolecular distance. The other attractive terms... 

The popular concept of bonding taking into consideration the ionic and covalent nature of chemical bonds agrees well with the partitioning presented above. Electrostatic forces represent ionic, while the delocalization term represents the covalent character of chemical bonds or interactions. Modem studies often consider the exchange repulsion interactions as a third component of the ionic-covalent concept of bonding [38]. 

In RCs where Bg is exchanged for [3-vinyl]-13 -hydroxy-bacteriochlorophyll a and then spheroidene-reconstituted, a MIA band shifts from 813 to 776 nm. This bleaching which has also been observed by MODS spectroscopy (Lous and Hoff, 1989) may be explained by a partial delocalization of the triplet excitation between spheroidene and Bg and allows the unequivocal determination of the ground state absorption of Bg (812 nm) which is obscured by the absorption of Ba (804 mn) and tbe upper exciton component of PV70 around 807 mn (Hartwich et al., 1995). The conclusion from these observations are that ... 

Results presented in the Table 6 indicate that the physical nature of pKa shifts is dominated at least in 99.8% by electrostatic term, with very small contribution of delocalization term not exceeding 0.2 %, whereas exchange component is completely negligible. Inexpensive atomic multipole estimates of the electrostatic term ApK may reasonably approximate costly SCF... 

It appears that in the case where minimum contacts R are quite short the electrostatic term still dominates, but this time delocalization and exchange components are not negligible and atomic multipole estimate (M)... 

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