  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.
