Bond energy models

Figure 17.5 Phase diagrams for the nearest-neighbor bond-energy model for the b.c.c.

Using the simple bond-energy model and potential functions introduced in Chapter 3, we attempt to estimate the bulk modulus, the thermal expansion coefficient, and the linear elastic coefficient with varying degrees of success. 

The Tersoff potential was designed specifically for the group 14 elements and extends the basic empirical bond-order model by including an angular term. The interaction energy between two atoms i and j using this potential is ... 

This model is appropriate for random mixtures of elements in which tire pairwise bonding energies remain constant. In most solutions it is found that these are dependent on composition, leading to departures from regular solution behaviour, and therefore the above equations must be conhned in use to solute concentrations up to about 10 mole per cent. 

Representing a heteropolymer, the model tries to capture tliree contributions to the overall energy E of each conformation the self-energy e of each amino acid, a bond energy tenn Ji i+i between two neighboring residues, and a nonbonded Ki j interaction... 

We often refer to Heitler and London s method as the valence bond (VB) model. A comparison between the experimental and the valence bond potential energy curves shows excellent agreement at large 7 ab but poor quantitative agreement in the valence region (Table 4.3). The cause of this lies in the method itself the VB model starts from atomic wavefunctions and adds as a perturbation the fact that the electron clouds of the atoms are polarized when the molecule is formed. 

Formula for the chemical potentials have been derived in terms of the formation energy of the four point defects. In the process the conceptual basis for calculating point defect energies in ordered alloys and the dependence of point defect concentrations on them has been clarified. The statistical physics of point defects in ordered alloys has been well described before [13], but the present work represents a generalisation in the sense that it is not dependent on any particular model, such as the Bragg-Williams approach with nearest neighbour bond energies. It is hoped that the results will be of use to theoreticians as well as... 

Hydrogen can decrease the strength of the metal-metal bond, thereby facilitating brittle fracture. Both the decohesion and surface energy models are based on this premise. 

Hall, C. M., 96, 373 Halogens atom models, 98 bond energies, 355 chemistry, 98 color, 352 covalent bonds, 97 covalent radius, 355 electron configuration, 352 ionization energies, 353 oxyacids, 358... 

---