Core charges

The ground-state electronic diagrams of some thiazolo dyes have been calculated with the use of theoretical model of fractional core charge model applied to PPP method (659). 

Ground state electronic diagram (Fractional core charge model within PPP framework) 43... 

As in the case of the free bases, the substitution of a nuclear hydrogen atom by a methyl group induces a bathochromic shift that decreases in the order of the position substituted 4->5->2- Ferre et al. (187) have proposed a theoretical model based on the PPP (tt) method using the fractional core charge approximation that reproduces quite correctly this Order of decreasing perturbation. 

I means the valence state ionization potential for the atomic orbital n, stands for the core charge, and Cj, and Xm are coefficients and atomic orbitals in the LCAO expansion... 

Thus, the current semi-empirical methods (MNDO, AMI and PM3) differ in the way in which core-repulsions are treated. Within the MNDO formalism the corerepulsion ( asmndo) is expressed in terms of two-centre, two-electron integrals (Eq. 5-4), where Za and Zb correspond to the core charges, Rab is the internuclear separation, and a a and aB are adjustable parameters in the exponential term [19]. 

L.E.D.C. Low Energy Detonating Cord. A detonating fuse with a core charge too low to enable it to be used reliably for initiating high explosives (see p. 124). 

The valence state ionization potential —the resonance integrals and the one-center electron repulsion integrals can be considered as basic parameters of the semiempirical method and can be adjusted to give optimal agreement. The core charges Z, indicate the number of 71 electrons the center M contributes to the n system, and the two-center electron repulsion integrals are obtained from an empirical relationship such as the Mataga-Nishimoto formula ... 

Now we go along with an argument offered by Tmhlar et al. [84]. In the evaluation of Eq. (4.33), and consistent with the nonoverlapping core orbitals assumption, we can neglect the core-other core exchange interactions. Because the core charge densities p (r) = 2 < (r)< (r) are spherically symmetric about their... 

Core Explosives or Core Charges. In ordet to lower the temperature of explosion to the level of "permissible explosives, thus avoiding the ignition of firedamp and dust in coal mines, R.W. Lawrence of Hercules Powder Co proposed [USP 2565380(1951) CA 46, 1752(1952)] to place inside of an AN Dynamite cartridge a "core , which can be either hollow or consist of an "inert material, similar to that used for sheaths (See under Enveloped or Sheathed Explosives)... 

Localization energies for electrophilic substitution were also calculated for a number of systems and were found to be in accord with experimental data. In these calculations a model was used with a core charge of 1 on both nitrogen and boron. In (3) the 3-position was predicted to be the most reactive to electrophilic substitution, in (17) the 2-position and in (16) the 3-position. These predictions were also made by Carbo using Fukui s superdelocalizability. 

In the right-hand side of this equation the first term takes into account the contributions to the exothermicity that are not associated with the medium, the second and the third terms the contributions from the interactions of the donor and the acceptor cores with the medium in the initial and the final states, respectively, and the fourth term the contribution from the unscreened Coulomb interaction between the donor and the acceptor, zx and z2 being the core charges of the donor and the acceptor, respectively. We must stress that, in the denominator of the last term of eqn. (59) the dielectric permeability of the medium is absent because the effect of the medium is contained in the terms E and E. If the distance between the donor and the acceptor considerably exceeds the sizes of the donor and the acceptor then, using eqn. (58), it is easy to obtain... 

It can be shown [24] that, in this situation, the dependence of the reaction exothermicity on if is also determined by eqn. (60) but with the following corrections for z one has to take not the core charge of the donor, but the full charge of the donor before the electron transfer has taken place for z2 one has to take the charge of the acceptor after the electron transfer has taken place. The dielectric permeability of the liquid solution should again be used as e, in eqn. (60). 

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