I want to output the pairwise force of lubrication interaction by the command “compute pair/local”, but LAMMPS reports ERROR: Pair style does not support compute pair/local. Since this pair style does not have a sing() function.
I have two questions: 1. Why doesn’t this potential have a single function? The lubrication force and torque are pairwise. 2. Is it possible to add a single function to the pair_lubricate.cpp file? In the source file I only found the expressions for the components of the force f[i][0], f[i][1], f[i][2], without the analytical expression of the resultant force.
This is an optional feature and the authors of the pair style elected to not implement it. If the pair style computes a torque, then using the Pair::single() function makes limited sense, since there is no way to pass the torque. Also, if the pair computation requires some pre-computation or adjustment of global properties before doing the individual force/torque computations, then you cannot include those in a single() function of the pair style.
Technically, yes. Whether this is meaningful depends on the details of the pair style and that I cannot say without having a closer look and knowing more about the details of the theory that is implemented.