# skew box too large

Hello all users and developers,

I try to simulate a triclinic system with LAMMPS. I have a crystal structure of super-cell (4X4X4 unit cells) obtained from XRD (XYZ file).

When I prepare the data file for lammps run, I use the tilt factors and cell dimensions from Materials Studio lattice parameters for this file.

But, then when I try to minimize I get the error of box skew is too large. How should I modify one of the tilt factors accordingly so the geometry

of the lattice stays the same ?

Thanks !

The Fritz Haber Research Center for Molecular Dynamics
Institute of Chemistry
The Hebrew University of Jerusalem
Jerusalem, ISRAEL

Phone: +972-8656-8909

From Section 6.12 of the doc pages:

To avoid extremely tilted boxes (which would be computationally
inefficient), no tilt factor can skew the box more than half the
distance of the parallel box length, which is the 1st dimension in the
tilt factor (x for xz). For example, if xlo = 2 and xhi = 12, then the
x box length is 10 and the xy tilt factor must be between -5 and 5.
Similarly, both xz and yz must be between -(xhi-xlo)/2 and
+(yhi-ylo)/2. Note that this is not a limitation, since if the maximum
tilt factor is 5 (as in this example), then configurations with tilt =
..., -15, -5, 5, 15, 25, ... are geometrically all equivalent. If the
box tilt exceeds this limit during a dynamics run (e.g. via the fix
deform command), then the box is "flipped" to an equivalent shape with
a tilt factor within the bounds, so the run can continue. See the fix
deform doc page for further details.

You just need to choose an equivalent tilt factor that is within the limits.

Steve