# 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¶

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  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)


rCut, C