Nature Of Interatomic Forces Research Articles

Cationic and anionic composition-dependent mechanical and thermal properties of zinc-blende specimens under $${\hbox {Mg}}_{x} {\hbox {Zn}}_{1\hbox {-}x} {\hbox {S}}_{y} {\hbox {Se}}_{1\hbox {-}y}$$ quaternary system: calculations with density functional FP-LAPW scheme

Elastic and thermal properties of zinc-blende $${\hbox {Mg}}_{x} {\hbox {Zn}}_{1\hbox {-}x} {\hbox {S}}_{y} {\hbox {Se}}_{1\hbox {-}y}$$ quaternary alloys and their constituent binary/ternary compounds have been computed through first principles calculations. Elastic stiffness constants of specimens have been increased almost linearly with increasing sulfur composition at any fixed magnesium composition, while reverse trends have been observed with increasing magnesium composition at any fixed sulfur composition in each binary–ternary/ternary–quaternary system. Hardness of specimens has been increased almost linearly with increasing sulfur composition at any fixed magnesium composition, while it has been decreased with increasing magnesium composition at any fixed sulfur composition in each system. Mechanical stability, elastic anisotropy, compressibility, ductility and plasticity have been observed in each compound. Mixture of covalent and ionic bonding with prominent role of covalent nature, dominating role of bond bending over stretching and central nature of interatomic forces have been investigated in each compound. Interaction between the atoms in any compound has been observed to be anharmonic in nature via calculated Gruneisen parameter. Computed Debye temperature, Debye frequency, thermal conductivity and melting temperature of all the specimens have also been reported.

Stability analysis of carbon nanotubes using a hybrid atomistic-structural element

In this paper, a hybrid atomistic-structural element for studying the mechanical behaviour of carbon nanotubes is introduced. Non-linear formulation for this element is derived based on empirical inter-atomic potentials. This hybrid element is capable of taking into account the non-linear nature of inter-atomic forces as well as the non-linearity arising from large deformations. Using these capabilities, the stability analysis of carbon nanotubes under axial compressive loading is performed and the post-buckling behaviour is predicted. Also, the dependence of axial buckling force on nanotube radius is shown.

Finite element evaluation of lattice distortions around hydrogen occupied interstitial sites in vanadium and niobium

Finite element evaluation of lattice distortions due to interstitial site occupancy by hydrogen in vanadium and niobium has been demonstrated. The finite element formulation has been based on the nature of interatomic forces. In contrast to previous models which require complex functions of the crystal lattice to describe distortion, the parameters used in the present finite element model are elastic constants of the host crystal lattice, its lattice parameter and the minimum potential energy distance between host crystal lattice atom and the interstitial atom. One of the major advantages of the present model is that the displacement of even the th nth neighbor away from the occupied interstitial site can be calculated. Displacements evaluated by the finite element analysis (FEA) and the previous theories have been compared. The advantage of using finite element method (FEM) to predict lattice distortions around occupied interstitial site has been highlighted.

Intrinsic Structure in Grain Boundaries and Boundary Mobility

An outstanding experimental contribution to the knowledge of grain boundary structure in the 1970's is the work of Balluffi and his colleagues at Cornell University on artificially fabricated boundary interfaces in thin films of gold (e.g., Balluffi, Komem and Schober, 1972; Balluffi, Goodhew, Tan and Wagner, 1975). In particular, for high-angle boundaries they have shown that secondary grain boundary dislocations (g.b.d's.) do exist and accommodate a deviation from a low-energy misorientation corresponding to an exact C.S.L. relationship. Further, following the results of Spyridelis, Delavignette and Amelinckx (1967) they have shown that a network of g.b.d's. can act as a diffraction grating, causing extra reflections whose spacing is reciprocally related to the separation of the g.b.d's. (Balluffi, Sass and Schober, 1972). The description of high-angle grain boundaries in terms of secondary g.b.d's. accommodating a departure from an exact C.S.L. orientation is based solely on geometrical considerations, but it has been pointed out that other low-energy configurations may be preferred when account is taken of the nature of interatomic forces (Gleiter and Pumphrey, 1976; Hermann, Gleiter and Baro, 1976; Smith, Vitek and Pond, 1977).

Piezoelectricity

It is shown that piezoelectric effects can be easily derived from bulk properties and are expressible in terms of linear and quadrupole moments of variations in charge density induced by atomic displacements. The linear-moment contribution is determined by optic macroscopic effective charges and internal-strain parameters. The remaining terms measure directly the induced quadrupole moment, and hence provide insight into the nature of interatomic forces and chemical bonding. Special attention is focussed upon the zinc-blende structure. An important step in the derivation is the use of translation and rotation invariance to transform the basic equations to eliminate convergence difficulties and give expressions manifestly independent of surface configurations.

Introduction

It was difficult to find a suitable title for this discussion, and perhaps I had better explain at the start why this particular title was chosen and what we shall try to discuss. We now know a good deal about the magnitude and nature of interatomic forces, and much of this knowledge has been acquired from the study of molecular spectra. Less is understood about the nature of intermolecular forces, although a number of experimental methods are being used to examine them. Among these methods, molecular spectroscopy again looks promising, probably because it is now possible to obtain a greater precision of measurement as regards the position and intensity of absorption bands or lines, so that small spectral variations which arise in different physical conditions can be detected. In this way, the effect of neighbour molecules upon an absorbing chromophore can be examined, and attempts can be made to interpret the interactions in terms of the appropriate energy levels. This is the leitmotif of our discussion.