Pair style polymorphic

Dear Lammps-Users,

I am writing to inquire if anyone has used the pair style polymorphic to allow for multi-angle minima in the three-body term.

I am able to implement the pair style for a standard Stillinger-Weber potential and minimize the structures to the correct angles. However, when I modify the G(theta) function to promote three minima or prefered angles, the structures do not minimize to the correct angles. In fact, the structures minimize to the maxima of the given function. I have simplified my system such that there are only three particles, and have arranged the three particles to have starting configurations either close to or exactly at the preferred minima. And yet, the minimized, three particles still diverge to penalized angles.

I can send the input files or the plot of the three body function I am attempting to implement if that would be helpful. Thank you in advance for any feedback or help you can provide.


Samantha Walker

Attached are the files for the test, and I am running with lammps version 12Dec18. mW.poly is the standard Stillinger-Weber that succeeds. triple_well.poly is the modified G(theta) function that fails to minimize to the correct angles. min.npt is the input script I use for both. is the three-particles arranged at 148 degrees.

mW.poly (78.4 KB)

triple_well.poly (73.6 KB) (462 Bytes)

min.npt (1.12 KB)