source: src/Thermostats/Langevin.cpp@ aa8ef2

/*
 * Langevin.cpp
 *
 *  Created on: Aug 20, 2010
 *      Author: crueger
 */

// include config.h
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include "CodePatterns/MemDebug.hpp"

#include "Langevin.hpp"
#include "element.hpp"
#include "config.hpp"
#include "CodePatterns/Verbose.hpp"
#include "CodePatterns/Log.hpp"
#include "ThermoStatContainer.hpp"

#include "RandomNumbers/RandomNumberGeneratorFactory.hpp"
#include "RandomNumbers/RandomNumberGenerator.hpp"

Langevin::Langevin(double _TempFrequency,double _alpha) :
  TempFrequency(_TempFrequency),
  alpha(_alpha)
{
  gsl_rng_env_setup();
  T = gsl_rng_default;
  r = gsl_rng_alloc (T);
}

Langevin::Langevin() :
  TempFrequency(2.5),
  alpha(0.)
{}

Langevin::~Langevin()
{
  gsl_rng_free (r);
}

const char *ThermostatTraits<Langevin>::name = "Langevin";

std::string ThermostatTraits<Langevin>::getName(){
  return ThermostatTraits<Langevin>::name;
}

Thermostat *ThermostatTraits<Langevin>::make(class ConfigFileBuffer * const fb){
  double TempFrequency;
  double alpha;
  const int verbose = 0;
  ParseForParameter(verbose,fb,"Thermostat", 0, 2, 1, double_type, &TempFrequency, 1, critical); // read gamma
  if (ParseForParameter(verbose,fb,"Thermostat", 0, 3, 1, double_type, &alpha, 1, optional)) {
    DoLog(2) && (Log() << Verbose(2) << "Extended Stochastic Thermostat detected with interpolation coefficient " << alpha << "." << endl);
  } else {
    alpha = 1.;
  }
  return new Langevin(TempFrequency,alpha);
}

double Langevin::scaleAtoms(unsigned int step,double ActualTemp,ATOMSET(std::list) atoms){
  return doScaleAtoms(step,ActualTemp,atoms.begin(),atoms.end());
}

double Langevin::scaleAtoms(unsigned int step,double ActualTemp,ATOMSET(std::vector) atoms){
  return doScaleAtoms(step,ActualTemp,atoms.begin(),atoms.end());
}

double Langevin::scaleAtoms(unsigned int step,double ActualTemp,ATOMSET(std::set) atoms){
  return doScaleAtoms(step,ActualTemp,atoms.begin(),atoms.end());
}

template <class ForwardIterator>
double Langevin::doScaleAtoms(unsigned int step,double ActualTemp,ForwardIterator begin, ForwardIterator end){
  DoLog(2) && (Log() << Verbose(2) <<  "Applying Langevin thermostat..." << endl);
  RandomNumberGenerator &random = RandomNumberGeneratorFactory::getInstance().makeRandomNumberGenerator();
  const double rng_min = random.min();
  const double rng_max = random.max();
  double ekin=0;
  for(ForwardIterator iter=begin;iter!=end;++iter){
    double sigma  = sqrt(getContainer().TargetTemp/(*iter)->getType()->getMass()); // sigma = (k_b T)/m (Hartree/atomicmass = atomiclength/atomictime)
    Vector &U = (*iter)->Trajectory.U.at(step);
    if ((*iter)->FixedIon == 0) { // even FixedIon moves, only not by other's forces
      // throw a dice to determine whether it gets hit by a heat bath particle
      if (((((random()/(rng_max-rng_min)))*TempFrequency) < 1.)) {
        DoLog(3) && (Log() << Verbose(3) << "Particle " << (**iter) << " was hit (sigma " << sigma << "): " << U.Norm() << " -> ");
        // pick three random numbers from a Boltzmann distribution around the desired temperature T for each momenta axis
        for (int d=0; d<NDIM; d++) {
          U[d] = gsl_ran_gaussian (r, sigma);
        }
        DoLog(2) && (Log() << Verbose(2) << U.Norm() << endl);
      }
      ekin += 0.5*(*iter)->getType()->getMass() * U.NormSquared();
    }
  }
  return ekin;
}

std::string Langevin::name(){
  return ThermostatTraits<Langevin>::name;
}

std::string Langevin::writeParams(){
  stringstream sstr;
  sstr << TempFrequency << "\t" << alpha;
  return sstr.str();
}