Correlation, effects dissociation energies

The departure of the Eh values from a smooth trend is somewhat over half as large as that of the dissociation energy values in the last row of Table VI. Until the London energy calculations are refined to eliminate the dipole-dipole approximation and other uncertainties, it is not possible to say whether that effect accounts for the entire anomaly or not. In any event a substantial portion of the anomaly may be ascribed to the correlation of the motion of the unshared electron pairs in. the valence shell. 

Comparing the last two entries in Figure 4.7, the all-electron Douglas-Kroll coupled cluster result for A te is in perfect agreement with the RPPA [156, 157]. Figure 4.8 shows the relativistic effects in dissociation energies. Here, relativistic effects are very sensitive to the level of electron correlation and basis sets used. RPPA... 

CCSD(T) calculations predict a relativistic increase in the dissociation energy of 78kJmol [155]. In comparison, electron correlation increases the dissociation energy by 134kJ mol . Spin-orbit effects increase the dissociation energy further by about 3kJmol [158]. Thus we predict a ArDe value of about SOkJmol. A comparison of calculated force constants reveals a similar picture, see Ref. [131]. 

Figure 4.8 Relativistic increase ApDe in dissociation energy for Au2 calculated in the years from 1989 to 2001 using a variety of different quantum chemical methods. Electron correlation effects AcDg = De(corr.)—De(HF) at the relativistic level are shown on the right hand side of each bar if available. For details see Figure 4.7.

In an alternative assessment of the effectiveness of these computer programs, it was concluded that explosive power was over-emphasised in relation to the more practically important aspect of sensitivity to initiation, and many compounds were being indicated as hazardous when they were not. There was also no provision for considering polymerisation as a hazardous possibility, and there was little quantitative data on this. The parameter best correlating with material sensitivity is the bond-dissociation energy. It was recommended that regulations specifying the... 

A detailed discussion of the effects of sulfenyl, sulflnyl, and sulfonyl groups on acidities and homolytic bond dissociation energies of adjacent C—H and N—H bonds has included interpretation of the following Hammett-type correlations val-... 

For an explicit examination of the basis set superposition error on weakly bound cationic structures at various theoretical levels, we performed full counterpoise calculations as outlined in Section IIB (Table 5). Table 5 demonstrates nicely that the magnitude of the BSSE is indirectly proportional to the size of the basis set at TZ2P, the error is on the average only about a quarter of that at DZP. This effect becomes more apparent with increased incorporation of electron correlation. At our best theoretical level, the BSSE amounts to only 0.1 kcal mol" (Table 5), which is insignificant for the dissociation energy of about 1.5 kcal mol". ... 

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