Hi Steve,
I want to calculate a magnitude that includes Fij and Vi, (where Fij is a given two boddy force between two atoms i,j and Vi the velocity of one of these atoms) in the code itself (pair potential file). It seems that the velocities I get within the pair force calculation routine (compute()) are calculated at time steps that are shifted compared to the time steps where the forces are actually calculated. It seems there is a dt/2 time shifting (dt=time steps) between the two calculations.
e.g :
F calculated at 0, dt, 2dt, 3dt,…
V calculated at dt/2, 3/2dt, 5/2dt…
I think lammps uses a velocity verlet integrator, not a leapfrog one and I am confused :
I would like to know if it is actually the case and if so, how can I get the forces and the velocities calculated exactly at the same time steps (no extrapolation) through the compute routine ?
Thanks a lot for you time,
y/