forked from lijiext/lammps
66 lines
2.2 KiB
Python
66 lines
2.2 KiB
Python
from __future__ import print_function
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class LAMMPSPairPotential(object):
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def __init__(self):
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self.pmap=dict()
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self.units='lj'
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def map_coeff(self,name,ltype):
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self.pmap[ltype]=name
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def check_units(self,units):
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if (units != self.units):
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raise Exception("Conflicting units: %s vs. %s" % (self.units,units))
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class LJCutMelt(LAMMPSPairPotential):
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def __init__(self):
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super(LJCutMelt,self).__init__()
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# set coeffs: 48*eps*sig**12, 24*eps*sig**6,
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# 4*eps*sig**12, 4*eps*sig**6
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self.units = 'lj'
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self.coeff = {'lj' : {'lj' : (48.0,24.0,4.0,4.0)}}
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def compute_force(self,rsq,itype,jtype):
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coeff = self.coeff[self.pmap[itype]][self.pmap[jtype]]
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r2inv = 1.0/rsq
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r6inv = r2inv*r2inv*r2inv
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lj1 = coeff[0]
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lj2 = coeff[1]
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return (r6inv * (lj1*r6inv - lj2))*r2inv
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def compute_energy(self,rsq,itype,jtype):
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coeff = self.coeff[self.pmap[itype]][self.pmap[jtype]]
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r2inv = 1.0/rsq
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r6inv = r2inv*r2inv*r2inv
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lj3 = coeff[2]
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lj4 = coeff[3]
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return (r6inv * (lj3*r6inv - lj4))
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class LJCutSPCE(LAMMPSPairPotential):
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def __init__(self):
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super(LJCutSPCE,self).__init__()
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self.units='real'
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# SPCE oxygen LJ parameters in real units
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eps=0.15535
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sig=3.166
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self.coeff = {'OW' : {'OW' : (48.0*eps*sig**12,24.0*eps*sig**6,
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4.0*eps*sig**12, 4.0*eps*sig**6),
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'HW' : (0.0,0.0, 0.0,0.0)},
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'HW' : {'OW' : (0.0,0.0, 0.0,0.0),
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'HW' : (0.0,0.0, 0.0,0.0)}}
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def compute_force(self,rsq,itype,jtype):
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coeff = self.coeff[self.pmap[itype]][self.pmap[jtype]]
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r2inv = 1.0/rsq
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r6inv = r2inv*r2inv*r2inv
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lj1 = coeff[0]
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lj2 = coeff[1]
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return (r6inv * (lj1*r6inv - lj2))*r2inv
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def compute_energy(self,rsq,itype,jtype):
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coeff = self.coeff[self.pmap[itype]][self.pmap[jtype]]
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r2inv = 1.0/rsq
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r6inv = r2inv*r2inv*r2inv
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lj3 = coeff[2]
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lj4 = coeff[3]
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return (r6inv * (lj3*r6inv - lj4))
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