deformation in a nanorod

Dear Sir’s
i want to deform the nanorod by tensile deformation for which i am using command
fix 6 all deform 1 x vel 0.1 units box remap x units box

My problem is that how can i deform the rod in such a way that both ends of the rod are not effected during the deformation process and coordinates of only middle portion are remapped and deformed.

second part of my question is can i use fix deform command for causing a uni axial deformation in the rod?

Thanks in advance for any kind of help and suggestions

Imran
Ph.D Scholar

Hi Imran,

First, I assume that your nanorod is periodic in the x direction and
is finite in y and z.

[***
If it is also finite in x, then fix deform won't have any net effect.
On each timestep, after you shift the atoms in the x direction, they
will just snap back to their equilibrium positions. You can still
stretch a finite nanorod by defining two groups of atoms on the ends
and pulling on them, using say fix addforce.
***]

Because you have free surfaces in y and z , there is nothing to stop
the cross-section from shrinking or expanding in response to the
tensile deformation. So, this is not uniaxial strain, but it is close
to uniaxial stress. Anyway, this is also what happens in nature. You
might be able to do uniaxial strain by setting all y and z forces to
zero, but that would be very unphysical.

I do not understand your question about not deforming the ends. How
can you have tensile deformation without moving the ends? Maybe you
mean that you want the relative positions of atoms in the ends to be
unchanged. You can achieve this using fix setforce:

fix westendfix westend setforce -2.0 0.0 0.0
fix eastendfix eastend setforce 2.0 0.0 0.0

aidan