In my current simulations, I have two species of particles. The 1-1 and
2-2 interactions are coul/long, but the 1-2 interaction is a
hybrid/overlay potential that is the Coulomb potential *minus* a Debye
potential. I define the pair interactions by
pair style hybrid/overlay coul/long \{cutf\} coul/debye {alf} ${cutf}
pair coeff * * coul/long
pair coeff 1 2 coul/debye
fix soft all adapt 0 pair coul/debye scale 1 2 v_neg1 scale yes reset
no
The variable v_neg1 is just -1 stored in a variable. From past
experience, this approach works as intended to create the potential
v12(r) = q1q2/r (1 - exp(-\alpha r))
My question comes from recent simulations where my input script contains
multiple "run" commands. Schematically, the this part of the input file
looks like
run 500
fix kick all addforce 0 0 v_perturb every 1
run 1
unfix kick
run 1000
When I look at the total energy of the system, it *instantaneously
drops* at time step 500, then increases between 500 and 501 (due to the
perturbation) and then again instantaneously drops at 501. I speculate
that the second and third "run" invocations are re-applying the fix
adapt that sets the sign of the overlay for the 1-2 interaction. This is
corroborated by visualizing the simulation, in which some particles
"slingshot" when the (small) perturbation is applied.
I thought the point of the "reset no" keyword was to prevent fix adapt
from getting reapplied? Is my understanding wrong? I am using
lammps-19May17.
Cheers,
Nathaniel Shaffer
University of Iowa
Physics & Astronomy