Ab initio Investigation of Elasticity and Stability of Metal Aluminum

TL;DR

This study uses ab initio methods to analyze aluminum's elastic and stability properties under various stress conditions, revealing instability points, transformation limitations, and strength characteristics along different crystallographic directions.

Contribution

It provides detailed stress-strain data and stability analysis of aluminum using pseudopotential plane-wave methods, expanding the ab initio database for material modeling.

Findings

All considered structures are unstable and shear unstable except natural f.c.c.

Bain transformation from f.c.c. to b.c.c. cannot occur via uniaxial compression.

Higher biaxial extension increases stress and tensile strength, with little change in critical strain.

Abstract

On the basis of the pseudopotential plane-wave(PP-PW) method in combination with the local-density-functional theory(LDFT), complete stress-strain curves for the uniaxial loading and uniaxial deformation along the [001] and [111] directions, and the biaxial proportional extension along [010] and [001] of aluminium are obtained. During the uniaxial loading, certain general behaviors of energy versus stretch and the load versus the stretch are confirmed; in each acse, there exist three special unstressed structures: f.c.c., b.c.c. and f.c.t. for [001]; f.c.c., s.c. and b.c.c. for [111]. Using stability criteria, we find that all of these state are unstable, and always occur together with shear instability, except the natural f.c.c. structure. A Bain transformation from the stable f.c.c. structure to the stable b.c.c. configuration cannot be obtained by uniaxial compression along any equivalent [001] and [111] direction. The tensile strength are similar for the two directions. For the higher energy barrier of [111] direction, the compressive strength is greater than that for the [001] direction. With increase in the ratio of the biaxial proportional extension, the stress and tensile strength increase; however, the critical strain does not change significantly. Our results add to the existing ab initio database for use in fitting and testing interatomic potentials.