-deform <direction> <strain> <poisson>
or
-def <direction> <strain> <poisson>
This option allows to deform a system, either in tension or compression.
The user has to provide the direction of deformation, the applied strain, and the Poisson's ratio of the material. The program will then deform the material in the given direction according to the applied strain, and deform it in the other directions according to Poisson's ratio. This transformation should result in an uniaxial stress: the stress will be non-zero in one direction, but should be zero in the other directions (that is, if Poisson's ratio is specified correctly).
If you want to apply an uniaxial strain, then set Poisson's ratio to zero.
If you want to use an anisotropic Poisson ratio, then use uniaxial strain to deform each direction accordingly.
The command-line parameters of importance are:
Default is <strain> = 0 (i.e. the system is not deformed at all).
pikashu initial.cfg final.xyz -deform x 6 0.3
This will elongate the system unitcell.cfg
by 6% along X, applying a Poisson's ratio of 0.3 along the other axes; this is equivalent to uniaxial stress. The result will be output into final.xyz
.
pikashu initial.cfg final.xyz -def y 2.5 0.0
This will apply an uniaxial strain (Poisson's ratio is 0) of 2.5% along Y to the system unitcell.cfg
. The result will be output into final.xyz
.
pikashu initial.cfg final.xyz -def x 1 0 -def y -0.7 0 -def z -0.68 0
This will apply an uniaxial deformation of 1% along X, and compress the system by 0.7% along Y and 0.68% along Z. This is equivalent to using a non-isotropic Poisson ratio.