# espressopp.interaction.FENECapped¶

A capped FENE potential avoiding calculation of unreasonably large bonded forces. It is usually applied at the equilibration stage of a simulation and helps a polymer system to relax. After the system has reached its equilibrium the capped potential should be substituted by a regular FENE, espressopp.interaction.FENE.

The capped FENE potential is employed as:

$U = -\frac{1}{2}r_{max}^2 K \cdot log \left[1 - \left(\frac{D - r_0}{r_{max}}\right)^2\right],$

where

$D = min \left(r, r_{\it{cap}}\right).$
class espressopp.interaction.FENECapped(K = 30.0, r0 = 0.0, rMax = 1.5, cutoff = inf, r_cap = 1.0, shift = 0.0)
Parameters: K (real) – attractive force strength (in $$\epsilon / \sigma^2$$ units) r0 (real) – displacement parameter (in $$sigma$$ units) rMax (real) – size parameter (in $$sigma$$ units) cutoff (real) – cutoff radius r_cap (real) – radius of capping (in $$sigma$$ units) shift (real) – shift of the potential

After setting up the potential you have to apply it to the particles in the pair list (bondlist):

class espressopp.interaction.FixedPairListFENECapped(system, bondlist, potential)
Parameters: system (object) – system object espressopp.System() bondlist (list) – list of bonds espressopp.FixedPairList() potential (object) – bonded potential, in this case espressopp.interaction.FENECapped()

Methods

getFixedPairList()
Return type: A Python list of pairs (the bondlist)
getPotential()
Return type: potential object
setFixedPairList(bondlist)
Parameters: bondlist (list) – fixed-pair list (bondlist)
setPotential(potential)
Parameters: potential (object) – a potential applied to all pairs in the bondlist

Example of usage

>>> Please, refer to the example of FENE potential


Go to FENE-example espressopp.interaction.FENE