forked from lijiext/lammps
63 lines
1.8 KiB
C
63 lines
1.8 KiB
C
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#ifndef CBLJCUT_H
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#define CBLJCUT_H
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#include <iostream>
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#include <cstdlib>
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#include "CbPotential.h"
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namespace ATC
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{
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/**
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* @class CbLjCut
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* @brief Class for computing Cauchy-Born quantities for a Lennard-Jones/cut material
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* (A factor of one-half is already included to split the
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* bond energy between atoms)
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*/
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class CbLjCut : public CbPotential
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{
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public:
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//! Constructor - initializes coefficients and enables PAIRWISE term.
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CbLjCut(double eps, double sig, double cutoff_radius)
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: CbPotential(Interactions(PAIRWISE)),
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A (4.0*eps*pow(sig, 12)),
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B (4.0*eps*pow(sig, 6)),
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rcut(cutoff_radius)
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{ }
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//! Returns the cutoff readius of the LJ potential.
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double cutoff_radius() const { return rcut; }
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//! Returns the LJ energy between two interacting atoms (6,12).
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double phi(const double &r) const
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{
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const double r6i = 1.0/((r*r*r)*(r*r*r));
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return r6i*(A*r6i - B);
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}
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//! Returns the first derivative of the LJ energy (7,13).
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double phi_r(const double &r) const
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{
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const double ri = 1.0/r;
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const double r6i = (ri*ri*ri)*(ri*ri*ri);
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return r6i*ri*(6.0*B - 12.0*A*r6i);
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}
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//! Returns the second derivative of the LJ energy (8,14).
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double phi_rr(const double &r) const
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{
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const double r2i = 1.0/(r*r);
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const double r6i = r2i*r2i*r2i;
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return r6i*r2i*(13.0*12.0*A*r6i - 7.0*6.0*B);
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}
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//! Returns the third derivative of the LJ bond energy (9,15).
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double phi_rrr(const double &r) const
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{
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const double r3i = 1.0/(r*r*r);
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const double r9i = r3i*r3i*r3i;
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return r9i*(8.0*7.0*6.0*B - 14.0*13.0*12.0*A*r3i*r3i);
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}
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const double A, B; //!< phi = Ar^-12 + Br^-6
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const double rcut; //!< cutoff force
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};
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}
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#endif
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