Fractional atomic charge

In the approximation (neglecting correlation effects) of a well-defined electron configuration with q electrons in definite orbitals 

Ftot — — -Enucl/electr + -Skin + Felectr/electr 

We have here chosen to consider the barycentre (21, 22) of all the states belonging to the configuration, in which case 

Enucl/electr — 2 Eelectr/electr — kin = Etot Eelectr/electr (8) 

The parameters of interelectronic repulsion A ( , ) for two orbitals with highly different average radii are approximately V 1 hartree/bohr (this unit corresponds to 14.4 eV/A) of the largest orbital with the smallest average reciprocal 

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The possible existence of quark matter, meaning elements with fractional atomic charges has been examined in a number of publications. Among them are some articles by C.K. Jorgensen (20). 

Moreover, topological atomic valencies TAVs, or corrected second moments) were derived from fractional atomic charges by rescaling the values with respect to the 2 -order molecular self-returning walk count srw ... 

Fractional total charge weighted partial positive surface area Fractional atomic charge weighted partial positive surface area Fractional partial negative surface area... 

In collaboration with experimental groups, we have recently studied some chlorinated-benzene crystals, 1,2,4,5-tetrachlorobenzene (TCB) [59] and 1,4-dichlorobenzene (DCB) [60], as well as solid tetracyanoethene (TCNE) [58]. In these studies we have used empirical atom-atom potentials, of exp-6 type [see Eq. (6)], which we have supplemented with the Coulomb interactions between fractional atomic charges. Lattice dynamics calculations have been performed by the harmonic method, with inclusion of intramolecular vibrations [70], see Eqs. (17) to (24). The normal modes of the free molecules have been calculated from empirical Valence Force Fields, using the standard CF-matrix method [101, 102]. The results of these calculations are used here to illustrate some phenomena occurring in more complex molecular crystals. These phenomena are well known the numerical results show their quantitative importance, in some specific systems. 

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