potentials.py
7caf6cf459d3master

potentials.py
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			from __future__ import print_function

			class LAMMPSLJCutPotential(object):

			def __init__(self):
			self.pmap=dict()
			# set coeffs: eps, sig, 48epssig*12, 24epssig*6,
			# 4epssig*12, 4epssig*6
			self.coeff = {'lj' : {'lj' : (1.0,1.0,48.0,24.0,4.0,4.0),
			'NULL': (0.0,1.0, 0.0, 0.0,0.0,0.0)},
			'NULL': {'lj' : (0.0,1.0, 0.0, 0.0,0.0,0.0),
			'NULL': (0.0,1.0, 0.0, 0.0,0.0,0.0)}}

			def map_coeff(self,name,type):
			if name in self.coeff:
			self.pmap[type] = name
			else:
			raise Exception("cannot match atom type %s" % name)

			def compute_force(self,rsq,itype,jtype):
			coeff = self.coeff[self.pmap[itype]][self.pmap[jtype]]
			r2inv = 1.0/rsq
			r6inv = r2invr2invr2inv
			lj1 = coeff[2]
			lj2 = coeff[3]
			return (r6inv * (lj1*r6inv - lj2))

			def compute_energy(self,rsq,itype,jtype):
			coeff = self.coeff[self.pmap[itype]][self.pmap[jtype]]
			r2inv = 1.0/rsq
			r6inv = r2invr2invr2inv
			lj3 = coeff[4]
			lj4 = coeff[5]
			return (r6inv * (lj3*r6inv - lj4))