#ifndef excor_h
#define excor_h

/** \file excor.h
 * Header file for \ref excor.c
 * 
 * Contains declarations of the functions implemented in \ref excor.c,
 * enumeration if density polarised or not UnPolarised and ExCor parameter
 * structure.
 * 
  Project: ParallelCarParrinello
  Jan Hamaekers
  2000
  
  File: excor.h
  $Id: excor.h,v 1.14 2006/05/23 14:22:05 foo Exp $
*/

//! exchange and correlation energy for the polarised or unpolarised one.
enum UnPolarised {unpolarised,  //!< energy in SpinType#SpinDouble case (no polarisation)
                  polarised     //!< energy in SpinType#SpinUp/SpinType#SpinDown case (polarisation)
                 };  

/** Exchange correlation structure.
 * Contains simply all the parameters to evaluate the energy.
 */
struct ExCor {
  double gamma[2];    //!< un-/polarised parametrization value for \f${\cal E}_c \f$, \f$r_s \geq 1\f$
  double beta_1[2];   //!< un-/polarised parametrization value for \f${\cal E}_c \f$, \f$r_s \geq 1\f$
  double beta_2[2];   //!< un-/polarised parametrization value for \f${\cal E}_c \f$, \f$r_s \geq 1\f$
  double A[2];        //!< un-/polarised parametrization value for \f${\cal E}_c \f$, \f$r_s < 1\f$
  double B[2];        //!< un-/polarised parametrization value for \f${\cal E}_c \f$, \f$r_s < 1\f$
  double C[2];        //!< un-/polarised parametrization value for \f${\cal E}_c \f$, \f$r_s < 1\f$
  double D[2];        //!< un-/polarised parametrization value for \f${\cal E}_c \f$, \f$r_s < 1\f$
  double fac34pi;     //!< factor: \f$-\frac{3}{4\pi}\f$
  double facexrs;     //!< factor: \f$-\frac{3}{4\pi} (\frac{9\pi}{4})^{1/3}\f$
  double epsilon0;    //!< set to MYEPSILON
  double fac6PI23;    //!< factor: \f$(\frac{6}{\pi})^{2/3}\f$
  double facPI213;    //!< factor: \f$(\frac{\pi}{2})^{1/3}\f$
  double fac3PI23;    //!< factor: \f$(3\pi)^{2/3}\f$
  double fac6PIPI23;  //!< factor: \f$(6\pi^2)^{2/3}\f$
  double fac243;      //!< factor: \f$(2)^{4/3}\f$
  double fac1213;      //!< factor: \f$(\frac{1}{2})^{1/3}\f$
};

double Calcrs(struct ExCor *EC, double p);
double CalcZeta(struct ExCor *EC, double pUp, double pDown);
double CalcSEXr(struct ExCor *EC, double rsUp, double rsDown, double pUp, double pDown);
double CalcSE_GC(struct ExCor *EC, double p, double Dp);
double CalcSVVXr(struct ExCor *EC, double rs, enum SpinType ST);
double CalcSVVVXr(struct ExCor *EC, double rs, enum SpinType ST);
double CalcSECr(struct ExCor *EC, double rs, double zeta, double p);
double CalcSVVCr(struct ExCor *EC, double rs, double zeta, enum SpinType ST, double pUp, double pDown);
double CalcSVVVCr(struct ExCor *EC, double rs, double zeta, enum SpinType ST, double pUp, double pDown);
void InitExchangeCorrelationEnergy(struct Problem *P, struct ExCor *EC);
void CalculateXCEnergyNoRT(struct Problem *P);
void CalculateXCEnergyUseRT(struct Problem *P);
void CalculateXCPotentialNoRT(struct Problem *P, fftw_real *HGR);
double CalculateXCddEddt0NoRT(struct Problem *P, fftw_real *PsiCD);
double DensityGradient(fftw_real *density, int i, struct LatticeLevel *Lev, struct Lattice *Lat);
#endif