nanowire

Hi,

I am trying to pull a nanowire in the longitudinal direction. For that I am using " fix npt " (to control pressure and temperature) and " fix deform " to defrom the nanowire.

For instance, if I pull it in y direction I want to keep stresses(pressures) zero in x and z direction. So, my y is period but x and z are not. I am using the following code :

fix equil all npt temp 10 10 0.04 x 0 0 1 z 0 0 1couple none
fix def all deform 1 y scale 1.20 remap x units box

But it gives me error saying it cannot do pressure control in a non-periodic dimensions. I need to allow stress in y direction to evolve as it keeps deforming. So, I cannot put instead :

fix equil all npt temp 10 10 0.04 y 0 0 1 couple none

If I don’t do any pressure control at all, it gives an error on that. Can anyone put some light on this ? Any response would be much appreciated !

Thanks,

  • Piyas

Hi Piyas,

If you want to npt ensemble with a non periodic structure. Use NULL for the pressure control in those directions and you can still control pressure in periodic direction this way.

Ilaksh

If you are not willing to risk the unusual, you will have to settle for the ordinary.

  • Jim Rohn

Thanks, Llaksh ! I tried and found out that NULL actually works for older versions lammps. Right now, I am running 3-June-2011 version. NULL used to work for earlier than 7-July-2010 versions.So, NULL has become an invalid command for newer versions.

I am using " fix nvt ". Even though I don’t control over pressure now but I pull the nanowire in uniaxial tension, the stress in that direction evolves like it supposed to with other elements of stress almost close to zero. So, that’s serving the purpose !

  • Piyas

Thanks, Llaksh ! I tried and found out that NULL actually works for older
versions lammps. Right now, I am running 3-June-2011 version. NULL used to
work for earlier than 7-July-2010 versions.So, NULL has become an invalid
command for newer versions.

There is nothing the older version could do that the current version cannot.
In the newer version you specify exactly which box dimensions you
wish to barostat. Dimensions you do not specify are not barostatted,
which is the same as NULL in the older version.

Steve

Thanks, Steve !

  • Piyas