TICG pair potential

Overview

Define a pair potential energy function corresponding to the soft core repulsive potential with energy proportional to volume of intersecting spheres

\[\begin{split}V(r_{ij}) = \left[\begin{array}{cc} -C\frac{(r_{ij} - 2 R)^2 (r_{ij} + 4 R)}{16 R^3}, & r<r_{\rm cut}\\ 0, & r\geq r_{\rm cut} \end{array}\right.\end{split}\]

where \(r_{ij}\) is the distance between particles \(i,j\) \(C\) is potential strength, \(R\) is the sphere radius. Note that cutoff distance is two times \(R\).

parameters of potential can be defined directly within the python input script or read from a restart file.

Python Member Functions

Adding Fix

FixTICG(state=..., handle=...)

Arguments

state

state object to add the fix.

handle

A name for the fix.

Setting parameters from within the Python environment is done with setParameter.

setParameter(param=...,handleA=...,handleB=...,val=...,)

Arguments

param

name of parameter to set. Can be C, rCut.

rCut parameter has a default value equal to state.rCut. Note that R is half of rCut.

handleA, handleB

a pair of type names to set parameters.

val

value of the parameter.

it is possible to get value of the parameters within the Python environment with getParameter.

val = getParameter(param=...,handleA=...,handleB=...)

Arguments

param

name of parameter to set. Can be C, rCut.

handleA, handleB

pair of type names to set parameters for.

val

value of the parameter.

Examples

Adding the fix

#adding  TICG potential
ticg = FixTICG(state, handle='TICG')

Setting parameters in python

ticg.setParameter(param='eps', handleA='A', handleB='B', val=1.0)
ticg.setParameter(param='sig', handleA='B', handleB='B', val=1.0)

Setting same parameters for all types in python

#list of all types
types=['A','B','C','S','P','N']
for A in types:
for B in types:
    ticg.setParameter(param='C', handleA=A, handleB=B, val=1.0)
    ticg.setParameter(param='rCut', handleA=A, handleB=B, val=0.2)

Activating the fix

#Activate fix
state.activateFix(ticg)

LAMMPS data file parameter order

rCut, C