Vibrational properties of phonons in random binary alloys: An augmented space recursive technique in thekrepresentation

Abstract

We present here an augmented space recursive technique in the k-representation which include diagonal, off-diagonal and the environmental disorder explicitly : an analytic , translationally invariant , multiple scattering theory for phonons in random binary alloys. We propose the augmented space recursion (ASR) as a computationally fast and accurate technique which will incorporate configuration fluctuations over a large local environment. We apply the formalism to N i55P d45 , N i88Cr12 and N i50P t50 alloys which is not a random choice. Numerical results on spectral functions, coherent structure factors, dispersion curves and disordered induced FWHM's are presented. Finally the results are compared with the recent itinerant coherent potential approximation (ICPA) and also with experiments.

Thermal conductivity and diffusion-mediated localization in Fe1−xCrxalloys from first principles

“…The effects of dominant offdiagonal force constant disorder in alloys can be quite unusual, as we have shown earlier. 1 Most theories of thermal transport, developed in the past few decades however, are either based on the single-site coherent potential approximation (CPA), 2 the perturbation-based approach simulating the Peierls-Boltzmann equation (PBE) 3 or atomistic models with a large unit cell and periodic boundary conditions. 4 CPA, being a single-site mean-field approximation, is inadequate for treating multi-site off-diagonal disorder arising out of force constants and is reported, for example, to inadequately explain experimental life-time data on simple Ni-Pt alloys.…”

Phonons in disordered alloys: Comparison between augmented-space-based approximations for configuration averaging to integration from first principles

“…The two formalisms are the Augmented space recursion (ASR) [2] and the Itinerant coherent potential approximation (ICPA) [3]. The two different theories (DFPT-ASR and DFPT-ICPA) systematically provides a hierarchy of improvements upon the earlier single site based theories (like CPA etc.)…”

Anomalous random correlations of force constants on the lattice dynamical properties of disordered Au-Fe alloys

“…ASR is expected to correctly address both mass and force constant disorders, mainly in the higher frequency region, as demonstrated in our earlier papers. [24,31] Figure 1 also shows the phonon DOS, where the higher (lower) frequency region is dominated by Fe (Au), as expected by mass. It also explains the increase in number of states in the higher frequency region as the %Fe increases.…”

“…It has been described in great detail in earlier papers. [24,25] For a given size and symmetry cell, the SQS is used in conjunction with the small displacement method [26] to calculate the estimated force constants in a disordered alloy. ASR then performs the configurational averaging over a disorder environment, with these disordered force constants.…”