Synaptic order

Figure 5 equally displays the localization domains of aniline determined using the electron localization function technique (ELF)12,64, which defines the electronic basins within a molecular system. The basins correspond to the domains where electrons are localized either in paired bonds or in nonbonding lone pairs. In such a way, the number and nature of bonds between atoms could be determined. The ELF r)(r) value varies from 0 to 1 (0 < rj(r) < 1), which is chosen to determine the isosurfaces of the domains. Basins can be classified according to their synaptic order, that is, monosynaptic basins belong to the cores (denoted by C) whereas disynaptic basins describe the valence regions (denoted by V). 

This kind of analysis based on bifurcations is connected to the concept of synaptic order previously defined,47,49 and it has been applied to the study of electron localization in some simple chemical systems45 as it will be noted below. A recent application showing the usefulness of this type of analysis has been reported by Silvi concerning the bonding nature of the VOx and VOx+ (x = 1 — 4) molecular systems.50... 

Valence basin synaptic order 69 Valence shell charge 32 Vanadium compounds, as oxidants 1273-1278, 1286, 1288, 1312, 1313 Vancomycin 1315, 1321, 1324 resistance 1318... 

There are basically two types of basins. On the one hand are core basins organized around nuclei (with Z > 2) and on the other are valence basins in the remaining space. The structure provided by the core basins closely matches the inner atomic shell structure. A valence basin is characterized by its synaptic order which is the number of cores to which it is connected [36]. To be connected to a core a valence basin must fulfill the three following conditions ... 

Silvi and Gatti were interested in a direct space representation of the metallic bond and for that piupose performed periodic HF calculations on the bee lattices of Li, Na, K, V, and on the fee ones of Al, Ca, Sc, Cu. A topological analysis of p and of ELF reveals that, except for Al, the valence basins have a synaptic order larger than 2, and that the metallic bond appears to be a partial covalent bond, which is often multicentric and characterized by a low population of the valence basins (less than l.Oe ) and by synaptic orders as large as 6. 

As explained above, the cusp-type catastrophe between SSD-in and SSD-IV accounts for the V(H6) and Vi(05) monosynaptic basins being replaced by a single disynaptic basin V(05,H6), while the turning point between SSD-IV and SSD-V accounts for the change in the synaptic order of the disynaptic V(C3,05) basin to a new monosynaptic V3(05) basin. Hence, the whole population of the monosynaptic basins on 05, represented as V(05) in Fig. 10.8, decreases in the SSD-III to SSD-IV passage and increases back in the SSD-IV to SSD-V turning point. 

Silvi B (2002) The synaptic order a key concept to understand multicenter bonding. J Mol Struct 614(l-3) 3-10... 

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