State partial weak mixing

Completely different is the interaction of a Cu atom with the Ti rows. Here, in fact, not only is the bonding weak, but the spin density is also partially on Cu and partially on the surface atoms where the metal is adsorbed. This is due to the fact that on these sites the bonding is mainly due to the metal polarization induced by the surface electric field with little covalent bond at the interface. Again, there is a difference with respect to the Pd case, where a mixing of the 4d levels on Pd with the 3d empty states of the Ti cations leads to the formation of a relatively strong bond with a covalent polar character [38]. 

The sharp separation of CT solids in Fig. 2 into neutral (...DADA...) and ionic (...D A"D A"...) is not satisfied by several phenazine-TCNQ complexes whose ground states are best characterized as partly-ionic, with fractional q in mixed stacks. Partial ionicity raises both theoretical and experimental questions. The main theoretical problem for weakly-overlapping sites is that any one-electron treatment, even in the Hartree-Fock limit, yields a minimum energy for integral, rather than fractional q. Perturbing the individual molecular sites is not an attractive solution for small overlap. 

The symbols "T" and "R" stand for "tense" and "relaxed" the significance of this is explained in the next section.) An equilibrium between the T and R states is presumed to exist, and partial oxygenation shifts that equilibrium toward the R state. The shift is a concerted one (different from the sequential model above), so that mixed molecules with some subunits in the weak-binding state and some in the strong-binding state are specifically excluded. 

As in the case of the salts discussed above, appropriate pairs of cations and anions yield ionic liquids that are partially ordered but essentially nondimensional (OD) states [13]. In ionic liquids, the bulky geometries of both the cationic and the anionic species effectively prevent crystallization due to weak ionic interactions. Such ionic liquids can be converted to gelated materials. As an example, Guerrero-Sanchez and Schubert et al. investigated the gelation behavior of a quaternary ammonium ohgo(propylene oxide)-based ionic liquid 4 (Fig. 4.3a(i)) upon mixing with water... 

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