The Standard One-Period Bond Model

AbstractBased on structures determined by X-ray crystallography, ab initio MP2 calculations on type A mesoionic rings give geometries in good agreement with observed values. A study of four mesoionic ring systems, each with exocyclic oxygen, nitrogen or carbon groups, shows that the presence and configuration of exocyclic lone pairs significantly influences the geometry and configurational preference. Using a localised bond model and NBO analysis, these effects are rationalised in terms of an anomeric interaction of lone pairs with the antibonding orbitals of adjacent σ bonds. In agreement with experiment, similar effects are calculated for pyran-2-imines.

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Bond equilibrium theory for Te-rich liquid Tl–Te alloys

Canadian Journal of Chemistry ◽

10.1139/v77-269 ◽

1977 ◽

Vol 55 (11) ◽

pp. 1930-1936 ◽

Cited By ~ 2

Author(s):

Melvin Cutler

Keyword(s):

Free Energy ◽

Good Description ◽

Hole Concentration ◽

Enthalpy Of Mixing ◽

Dangling Bond ◽

Fermi Model ◽

Bond Model ◽

Independent Information ◽

Molecular Bond ◽

Rich Liquid

Recent work has provided independent information about the behavior of the hole concentration c in TlxTe1−x as a function of temperature T and composition x in the range 0.2 ≤ x ≤ 0.6. This makes possible a critical reexamination of a molecular bond model for the structure of the alloy, in which holes are generated by broken Te—Te bonds. The earlier theory is revised to formulate an unrestricted independent bond model (ibm), for which the equations are simple and have obvious physical interpretations. This provides a good description of c(T) but only a qualitatively correct c(x). Using a Thomas–Fermi model for the screening interaction between holes and the acceptor ions, it is shown that the equilibrium constant can be expected to increase rapidly with c at large enough values. A modification in which the free energy of a dangling bond is decreased by proximity to a Tl—Te bond is found to significantly improve the result for c(x). The thermochemical behavior is derived. The entropy of mixing is in fair agreement with experiment, but the enthalpy of mixing is grossly wrong. This reflects the neglect of intermolecular interactions in the theory, which, it seems, can easily account for the remaining discrepancies in the predicted behavior of c.

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A Review of some Theoretical Models for Point Defect Calculations

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.329.81 ◽

2012 ◽

Vol 329 ◽

pp. 81-0

Author(s):

Amitava Ghorai

Keyword(s):

Point Defect ◽

Discrete Model ◽

Continuum Model ◽

Theoretical Models ◽

Jellium Model ◽

Main Thrust ◽

Lattice Statics ◽

Bond Model ◽

Model Lattice ◽

Model Continuum

A Brief Sketch of Different Models for the Calculation of Defect Parameters in Metals and Alloys, Comparison of Data and Limitations Has Been Reviewed here; Especially Relaxations due to a Vacancy Type of Point Defect, its Formation, Migration, Activation Energies and Related other Parameters Based upon the Present Experimental Status. the Models Reviewed Are the Bond Model, Continuum Model, Semi-Discrete Model, Jellium Model, Thermodynamic Model, Lattice Statics Model, Atomistic Continuum Model and Pseudopotential Model. the Main Thrust Concerns the Last Model. the Taylor, Vashishta and Singwi, Harrison, Kleinmann and King and Kutler Form of Exchange and Correlation Function Are Almost Similar, Give Moderate Results and May Be Trusted for Better Results.

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