First-principles electronic structure calculations with molecular dynamics made easy

The technique of quantum molecular dynamics is reviewed, and a simplified approach based on a first-principles tight-binding implementation of local density theory is discussed. Several illustrations and applications of the theory are presented. Applying it to amorphous materials, we have developed a procedure for producing amorphous Si networks with small defect concentrations. Benchmark checks are made for atomic geometries at Si(111)-(2×1) and Si(001)-(2×1), p(2×2), and c(4×2) reconstructed surfaces. A simulation of a Scanning Tunneling Microscope tip interacting with a reconstructed surface is performed, and it is shown how the tip can alter the reconstruction of the surface. Simulation of a kinked Si(001) surface step and comparison to an unkinked step are also presented.     

Theory of electron spin resonance measurements of chalcogen pairs in Si

Calculations are presented which support the identification of two sulfur-related centers in Si (lying 0.37 and 0.19 eV below the conduction band minima) with (S, S)⁺ and (S, S)⁰ nearest-neighbor substitutional S pairs. Explanations in terms of $\text{meso-bonding}$ are given of the following facts: (i) Although S is much more electronegative than Si, the (S, S)⁺ pair level lies at higher energy than the S⁺ level by ? 0.2 eV; (ii) The hyperfine interaction for (S, S)⁺ is considerably smaller than for the isolated S defect; and (iii) The (S, S)⁺ molecular defect has a hyperfine tensor that is virtually isotropic.     

A new relaxation effect in gold-doped lead

Internal friction studies on gold-doped lead are reported which yield a relaxation time of τ = 10^-14.9exp 0.437 eV/kT. The defect producing the relaxation process appears to have 〈100〉 symmetry and a relatively large elastic-dipole strength. Since this activation energy is equal to that measured in diffusion it is suggested that the two processes are identical, presumably from a dumb-bell configuration.