Correlation energy experimental

Comparison of localization energies has frequently been applied to prediction of the relative positional reactivity in polycyclic aromatic hydrocarbons. Simple HMO calculations have only marginal success. CNDO/2 and SCF calculations give results which show good correlation with experimental data on the rate of proton exchange. ... 

There are a few other correction procedures that may be considered as extrapolation schemes. The Scaled External Correlation (SEC) and Scaled All Correlation (SAC) metiiods scale tire correlation energy by a factor such that calculated dissociation energy agrees with the experimental value. 

The magnitude of the core correlation can be evaluated by including the oxygen Is-electrons and using the cc-pCVXZ basis sets the results are shown in Table 11.9. The extrapolated CCSD(T) correlation energy is —0.370 a.u. Assuming that the CCSD(T) method provides 99.7% of the full Cl value, as indicated by Table 11.7, the extrapolated correlation energy becomes —0.371 a.u., well within the error limits on the estimated experimental value. The core (and core-valence) electron correlation is thus 0.063 a.u.. 

The evaluation of the preexponential term in eq. (100) for gas-phase reactions is straightforward. The absolute zero enthalpy, Eq, can be obtained either from semiempirical calculations on products and reactants or by means of ab initio calculations with a subsequent estimation of the correlation energy. In compromising treatments, the experimentally estimated enthalpies can be employed. 

Table IX presents both the theoretical ab initio energies of the components of reaction (102) and the experimental values which allow evaluation of the error introduced by neglecting the correlation energy.

The dimerization in exocyclic positions was considered. For the C-C a bond energy, we employed the value 82.17 kcal/mole for (3 unit, we used the value 15.8 kcal/mole obtained from the correlation of experimental and HMO delocalization energies. 

Unfortunately, the dynamic correlation energy is not constant for a given molecule but may vary considerably between different electronic states. Thus, any procedure geared towards quantitative accuracy in predicting excited-state energies must in some way account for these variations. The most economical way to achieve this is to introduce a number of parameters into the model. By scaling those to a set of experimental data... 

The excess energy of a real crystal fragment depends on how this was obtained usually, the fracture surface is imagined to be perfectly smooth, but real surfaces are rough, have steps, and so on. The surfaces assumed in theoretical calculations are not in contact with any other substance. If a gas, however, is admitted, then the unsaturated valencies will be saturated with adsorbed gas molecules, and the asymmetry of the field will be reduced. Thus the structure calculated for the external layer may be in equilibrium only in excellent vacuum, and the duration of this equilibrium would depend on how rapidly gases and vapors leak into the evacuated vessel. This remark shows, by the way, how illogical are the attempts to correlate the experimental estimates of ys or 7 with those calculated from the theories of Chapter II. 

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