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:

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