I am following the example for the calculation of elastic constants
provided by LAMMPS to calculate the elastic constants for magnesium. I
import my structure, rather that defining it manually . Apart from the
structure the only parameters I change is the mass and the potential.
When I use either displace_reverse.mod or displace_restart.mod I get an
error "ERROR: Cannot change box tilt factors for orthogonal box
This error appears after many successful minimisation calculations (and
many "Changing box ..."), but I am not sure I understand why it stops.
Could please give me a hint why?
You need to add dummy box tilt factors (with a value of 0) to your initial structure, so that it is considered as a triclinic box. This error happens when trying to use change_box with triclinic adjustable size parameters (xy, xz, yz) on an orthogonal box. Only (x, y, z) deformations can be defined for orthogonal boxes, which is why you saw several successful minimisations before the error.
In your structure file, you should therefore have this line after the xlo xhi ylo yhi zlo zhi lines :