2014 En utilisant la théorie des liaisons fortes, on calcule l'énergie de liaison Ebin, la relaxation des atomes et les densités d'états électroniques 03C1i(E) et de modes de vibration gi(03C9) pour des lacunes dans un métal de transition cubique centré. Nous utilisons un potentiel Born-Mayer pour représenter la répulsion de coeur dur entre voisins. Nous obtenons les énergies de liaison de bilacunes et de petits amas de lacunes (jusqu'a des tétralacunes) par un procédé direct de minimisation de l'énergie et nous comparons ces résultats aux expériences existantes. Avec la méthode de récursion de Haydock et al., nous calculons également les vibrations atomiques et la densité d'état d près d'un défaut lacunaire. En général, la relaxation du réseau atomique autour du défaut joue un rôle dominant dans la détermination des énergies de liaison et les modes de vibrations locaux. De plus, on montre que Ebin et 03C1i(E) sont très sensibles à la structure du défaut (configuration des lacunes). Le pic principal de résonance apparait au centre de la bande d de manière analogue à celui des états de surface observé sur W(001) ou 03B1-Fe(001) pour une tétralacune agrégée sur le plan (001).
Résumé. 2014 On étudie, dans l'approximation des liaisons fortes, la contribution électronique à l'énergie d'interaction entre atomes interstitiels en solution dans les métaux de transition (interaction I-I). La Abstract. -The electronic contribution to the interaction energy between interstitial solute atoms (I-I interaction) in transition metals is investigated within the tight-binding approximation. The theoretical method used in this study closely parallels that developed by Einstein and Schrieffer for the adatom interaction. The method permits us to study the solution of the gas atom in the octahedral sites as well as in the tetrahedral sites and also allows us to investigate the interaction between the interstitial and substitutional solute atoms (I-S interaction). Calculations have been carried out as a function of band filling, solute atom energy level, an impurity potential matrix element V0 on the substitutional atom site, and a général hopping potential Va between an interstitial atom and the nearest neighbour host atoms. The numerical results generally indicate the importance of the electronic contribution to the interaction énergies (both I-I and I-S interaction). Under reasonable conditions, our simple model of the I-S interaction is shown to agree well with the experimental data for Fe-based ternary alloys containing the simple gas atoms such as N or C. The angular position dependence of the I-I interaction energy is often weak and the possibility of the interstitial condensation (03B1-03B1' phase transition) observed in a Nb-H system is discussed. Contact is also made with the solute (I-I) interaction based on the elastic theory.
We use a tight-binding (TB) type electronic theory to calculate the core structure and core energy of both screw and 60° dislocations in the covalent semiconductors C, Si and Ge. To represent the repulsive interaction between atomic sites i and j, arising mainly from the core orthogonalization, we introduce a Born-Mayer potential. From the total (attractive and repulsive) energy calculations, we investigate the stability of dissociated partial dislocations. We show that the glide-set dissociated dislocations are more stable than the corresponding shuffle-set perfect dislocation, in agreement with recent experimental observations. The calculated results are also compared with available experimental results on the structure images and the dynamic properties of dislocations. In addition, we investigate the electronic states (sp configuration) of the dangling-bond-like states (DBLS) near the core of the partial dislocations, and discuss the validity of using fixed sp3 hybrid orbitals for calculating the dislocations.
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