Truncated Pair Force

class halmd.mdsim.forces.pair_trunc(args)

Construct truncated pair force.


The module computes the truncated potential forces excerted by the particles of the second particle instance on those of the first one. The two instances agree if only a single instance is passed. Recomputation is triggered by the signals on_force and on_prepend_force of args.particle[1].

The argument weight determines the fraction of the potential energy and the stress tensor that that is added to by the interaction of this force module. A value of 1 is defined as adding the full potential energy and stress tensor of each interaction. This is especially useful when considering pair forces where the particle instances (A and B) are distinct and only AB but not BA interaction is calculated.


If two different instances of halmd.mdsim.particle are passed, Newton’s 3rd law is not obeyed. To restore such a behaviour, the module must be constructed a second time with the order of particle instances reversed.

If trunc is not specified, the pair potential is C^0 continuous at the cutoff.

If neighbour is left unspecified, a default neighbour list module is constructed using the default parameters of halmd.mdsim.neighbour. If if a different value for, e.g., the occupancy parameter is needed, the neighbour list module has to be provided explicitly.


Instance of halmd.mdsim.potentials.


Disconnect force from profiler.


Currently this does not disconnect particle sorting, binning and neighbour lists.