lennard_jones.h

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/* ./continuum/libmesh/lennard_jones.h 
**********************************
Copyright INRIA and CEA 

author : Guillaume ANCIAUX (anciaux@labri.fr, g.anciaux@laposte.net)

The LibMultiScale is a C++ parallel framework for the multiscale
coupling methods dedicated to material simulations. This framework
provides an API which makes it possible to program coupled simulations
and integration of already existing codes.

This Project is done in a collaboration between INRIA Futurs Bordeaux
within ScAlApplix team and CEA/DPTA Ile de France. 

This software is governed by the CeCILL-C license under French law and
abiding by the rules of distribution of free software.  You can  use, 
modify and/ or redistribute the software under the terms of the CeCILL-C
license as circulated by CEA, CNRS and INRIA at the following URL
"http://www.cecill.info". 

As a counterpart to the access to the source code and  rights to copy,
modify and redistribute granted by the license, users are provided only
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economic rights,  and the successive licensors  have only  limited
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In this respect, the user's attention is drawn to the risks associated
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software by the user in light of its specific status of free software,
that may mean  that it is complicated to manipulate,  and  that  also
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***********************************/

#ifndef LENNARDJONES
#define LENNARDJONES

class LennardJones : public Potential<LennardJones>
{
 public:

  LennardJones(double _epsilon, double _sigma){
    epsilon =  _epsilon;
    sigma = _sigma;

    DUMP("setting lennard jones parameters : sigma = " << FORMATREAL(sigma)
        << " , epsilon = " << FORMATREAL(epsilon),DBG_INFO_STARTUP);
  };
  ~LennardJones(){};

  double ComputeForceFoisR(double inv_rr2){
    //    double rr2 = r*r;
    double rri2 = sigma*sigma * inv_rr2;
    double rri6 = rri2 * rri2 * rri2;
    DUMP("Computing force for inv_rr2=" << inv_rr2 << " : " << 24*epsilon*rri6*(1. - 2. * rri6),DBG_ALL);
    return 24*epsilon*rri6*(1. - 2. * rri6);
    }

  double ComputeForce(double r){
    double rr2 = r*r;
    double rri2 = sigma*sigma / rr2;
    double rri6 = rri2 * rri2 * rri2;
    DUMP("Computing force for r= " << r << " : " << 24*epsilon*rri6*(1. - 2. * rri6)/r,DBG_ALL);
    return 24*epsilon*rri6*(1. - 2. * rri6)/r;
    }


 private:
  double epsilon;
  double sigma;
};

#endif

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