I am trying to use the sw potential with three different atoms, and having
trouble figuring out how the cross terms are used. In addition, I am using
a hybrid potential where the interactions type2-type2, type2-type3, and
type3-type3 are overwritten with a tabulated potential after I read in the
entire sw file. Here is what I am finding with the sw potential.
I have run five simulations in which I have changed only the sw lines that
define when all three atoms are different... atom1 atom2 atom3, for example.
I'll call these "ijk" lines. When I read the help file / documentation for
the sw potential, it seemed that these weren't going to play a role. I set
the sigma values to be zero on these ijk lines as a consequence. In these
four simulations I changed only the sigma value to correspond to 0
angstroms, 3, 5, 7, and 9. (case0, case3, case5, case7, case9)
Case0, case3, and case5 come out to have the exact same trajectorys. Case3
takes twice as long as case0, and case5 takes about 5 times as long as
case0. Both case7 and case9 show different trajectories (they are different
from each other too). The average energies are the same, radial
distribution functions are the same, but they take of course much longer
I must conclude that the lines do play role, but it seems to only play a big
role in how much time it takes to perform the calculations. I'm wondering
how these lines are used by lammps. Also it makes me wonder if the sw
potential does get calculated for these type2-type2, etc interactions, even
though they are replaced through the hybrid style. I'm including below the
input file, as well as three representative sw files.
I appreciate any input to help understand what's going on here! Thanks,