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CauchyBorn.h
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Sun, Jun 2, 13:00

CauchyBorn.h
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#ifndef CAUCHYBORN_H
#define CAUCHYBORN_H
#include "CbPotential.h"
#include "MatrixLibrary.h"
#include "ATC_TypeDefs.h"
// This file provides all routines necessary for computing the Cauchy-Born
// stresses.
namespace ATC {
// forward declaration of CbPotential
class CbPotential;
class AtomCluster;
/**
* @class StressAtIP
* @brief Class for passing the vector of stresses at quadrature points
* Done by storing the quadrature point and providing indexing
*/
class StressAtIP {
INDEX q; //*> Quadrature point.
DENS_MAT_VEC &S; //*> Stress components at all quad points.
public:
//* Constructor - sets stress reference and current quadrature point.
StressAtIP(DENS_MAT_VEC &s, INDEX _q=0) : q(_q), S(s) {}
//* Indexing operator, gets stress components for the quadrature point.
double& operator()(INDEX i, INDEX j) const { return S[i](q, j); }
//* Sets quadrature point to a new index.
void set_quadrature_point(INDEX qp) { q = qp; }
//* Operator that outputs the stress
friend std::ostream& operator<<(std::ostream& o, const StressAtIP& s)
{ o << "stress\n";
o << s(0,0) << " " << s(0,1) << " " << s(0,2) << "\n";
o << s(1,0) << " " << s(1,1) << " " << s(1,2) << "\n";
o << s(2,0) << " " << s(2,1) << " " << s(2,2) << "\n";
return o;
}
};
/**
* @class StressArgs
* @brief Class for storing parameters needed for computing the Cauchy-Born stress
*/
class StressArgs {
public:
StressArgs(AtomCluster &v, CbPotential *p, double kB, double hbar, double T)
: vac(v), potential(p), boltzmann_constant(kB), planck_constant(hbar),
temperature(T) {}
AtomCluster &vac;
CbPotential *potential;
double boltzmann_constant;
double planck_constant;
double temperature;
};
/**
* @class PairParam
* @brief Class for storing parameters used in pairwise stress computations
*/
struct PairParam {
PairParam(const DENS_VEC &_R, double _d) : R(_R), d(_d), di(1.0/_d) {}
const DENS_VEC &R; //*> Reference bond vector.
DENS_VEC r; //*> Current bond vector.
double d, di; //*> Current bond length and its inverse.
double phi_r; //*> First derivative of pairwise term.
double phi_rr; //*> Second derivative of pairwise term.
double phi_rrr; //*> Third derivative of pairwise term.
double rho_r;
double rho_rr;
double rho_rrr;
double F_p;
double F_pp;
double F_ppp;
};
//* for EAM, calculate electron density
double cb_electron_density(const StressArgs &args);
//* Compute stress, from virtual atom cluster, potential
//* temperature (can be 0K), and StressAtIP object to write to.
void cb_stress(const StressArgs &args, StressAtIP &s, double *F=0);
//* Computes the elastic energy (free or potential if T=0).
double cb_energy(const StressArgs &args);
//* Computes the entropic energy
double cb_entropic_energy(const StressArgs &args);
//* Auxiliary functions for cb_stress
//@{
//* Computes the stress contribution given the pairwise parameters.
void pairwise_stress(const PairParam &p, StressAtIP &s);
//* Computes the stress contribution given the embedding parameters.
void embedding_stress(const PairParam &p, StressAtIP &s);
//* Computes the pairwise thermal components for the stress and free energy.
void pairwise_thermal(const PairParam &p, DENS_MAT &D, DENS_MAT_VEC *dDdF=0);
//* Computes the embedding thermal components for the stress and free energy.
void embedding_thermal(const PairParam &p, DENS_MAT &D, DENS_MAT &L0, DENS_MAT_VEC *dDdF=0);
//* Last stage of the pairwise finite-T Cauchy-Born stress computation.
void thermal_end(const DENS_MAT_VEC &DF, const DENS_MAT &D, const DENS_MAT &F,
const double &T, const double &kb, StressAtIP &s, double *F_w=0);
//* Returns the stretch tensor and its derivative with respect to C (R C-G).
void stretch_tensor_derivative(const DENS_VEC &C, DENS_VEC &U, DENS_MAT &dU);
//@}
//* Testing functions (to be removed when all CB code is completed)
//@{
//* Computes the dynamical matrix (TESTING FUNCTION)
DENS_MAT compute_dynamical_matrix(const StressArgs &args);
//* Computes the determinant of the dynamical matrix (TESTING FUNCTION)
double compute_detD(const StressArgs &args);
//* Computes the derivative of the dynamical matrix (TESTING FUNCTION)
DENS_MAT_VEC compute_dynamical_derivative(StressArgs &args);
//@}
}
#endif

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