Migration energy calculations

On another hand, migration energies calculated in Ref. [6] differ significantly from the isothermal residual resistance recovery measurements obtained by authors in Refs. [5] (0.45 eV), [10] (0.43 eV) and from the Gorsky effect determination with self-diffusion of H in Lu [11] (0.575 eV). Why does such a discrepancy exist ... 

The calculation of thermodynamic properties is difficult using MD techniques. The case of defects is especially problematic and both formation and migration energies are far more effectively calculated using static simulation techniques. 

One of the oldest and most successful fields of application of simulation techniques in solid state science concerns the study of defects in solids which, of course, influence many key properties including transport, reactivity and mechanical behaviour. Simulation techniques have been used with success for over 20 years in calculating formulation and migration energies of defects in solids. An account of the present state of the art is given in Chapter 7. 

We caimot assume that all the ions have found their ideal sites in sintered material, e.g., some AP" ions in MgAl204 may be on tetrahedral sites. The structure predicted by computer modeling for the [112 lateral twin interface in NiO contains a rigid-body translation. Such a translation is not observed experimentally for the same type of interface in spinel, which has the same oxygen sublattice. It may be that the reason for this difference is that the translation-free configuration is what is present on a migrating GB and this becomes frozen in when the sample is cooled. The structure predicted by minimum energy calculations is a stationary structure. 

The field developed rapidly in the 1970s, with applications of the technique to both halide [7, 8] and oxide [9-11] crystals which demonstrated the qualitative reliability of the method for calculating both formation and migration energies of defects, given reliable interatomic potentials. 

Fig. 4. Contour plot of the potential-energy surface for oxygen-vacancy migration, showing the curved path between adjacent anion sites of a BO octahedron (in the ab plane), b Calculated migration energy as a function of the tolerance factor (from both the A and B site simulations)...

Theoretical studies on four- and five-coordinate palladium(ii) model complexes containing a methyl, carbonyl, and methoxide ligand have been carried out, and the results obtained are in agreement with the above experimental observations. A kinetic and thermodynamic preference for insertion into the Pd-OMe bond over Pd-Me is found. The activation energy for methoxide migration was calculated to be between 33 and 42 kj mol compared to 62 and 73 kj moP for methyl migration in the same complexes. 

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