ERROR: Triclinic box skew is too large for Gamma glycine


Gamma glycine’s experimental lattice parameters are:
a = 6.86174
b = 6.86174
c = 5.42826
alpha = 90
beta = 90
gamma = 120

based on these, the box size and tilt factors are:

0 6.86174 xlo xhi
0 5.942441154163835 ylo yhi
0 5.42826 zlo zhi
-3.4308699999999988 3.323850616969806e-16 5.757078145360861e-16 xy xz yz

Throughout my tests, I learned that minimization with Triclinic external pressure and the equilibration run with NPT and isotropic barostat work well for getting a stable lattice for Alpha and Beta glycine.
However, this protocol fails for Gamma glycine and equilibration finished with an error as:
triclinic box = (0.17746561 -0.14569645 -0.13308978) to (20.407754 17.97302 16.41787) with tilt (-10.242392 -0.032297956 0.004965776)
ERROR: Triclinic box skew is too large (…/domain.cpp:217)

As I used a 333 box, tilt factors go up to -10. Previous discussions on this matter suggested lowering the tilt factors however, I can’t do that because that will change the lattice structure.
Any suggestions?

Kindest regards,

See box command — LAMMPS documentation

You can completely avoid these issues by using a super cell. At 90/90/120 degrees cell angles that should be particularly simple. If you double your primitive cell in z direction, you can switch to a 0 tilt since the total tilt will be exactly the amount of one box length in x, and thus the geometry will be the same. High tilt angles can lead to incorrect/incomplete neighbor lists and thus should be avoided. 120 degrees is the limit that LAMMPS uses, for most cases, if you go above, the cell tilt will be switched to opposite sign (while the atoms stay in their location). This is also how LAMMPS implements continuous shearing with fix deform.