Hello, I'm seeking clarification on the selection of suitable boundary conditions for simulating shear deformation of a screw dislocation using LAMMPS. In my script, I currently employ the following commands:

```lammps

fix 1 upper setforce 0.0 0.0 0.0

fix 2 lower setforce 0.0 0.0 0.0

fix 3 upper move NULL ${strainrate} NULL

fix 4 lower move NULL-${strainrate} NULL

fix 5 mobile nve

```

I have several uncertainties:

1. Should I fix all three degrees of freedom in fix 1 & 2 for shear deformation in the Y direction, or are specific degrees of freedom recommended?

2. In fix 3 & 4, should I use NULL or 0.0?

3. Should fix 5 be applied to only middle atoms or to all atoms?

Any insights would be greatly appreciated!