/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   http://lammps.sandia.gov, Sandia National Laboratories
   Steve Plimpton, sjplimp@sandia.gov

   Copyright (2003) Sandia Corporation.  Under the terms of Contract
   DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
   certain rights in this software.  This software is distributed under
   the GNU General Public License.

   See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */

/* ----------------------------------------------------------------------
   Contributing author: Georgios G. Vogiatzis (CoMSE, NTU Athens),
     gvog@chemeng.ntua.gr
 ------------------------------------------------------------------------- */

/* ----------------------------------------------------------------------
   Description:   This file implements the improper potential introduced
                  by Destree et al., in Equation 9 of:
                  - M. Destree, F. Laupretre, A. Lyulin, and J.-P.
                    Ryckaert, J. Chem. Phys. 112, 9632 (2000),
                  and subsequently referred in:
                  - A.V. Lyulin, M.A.J Michels, Macromolecules, 35, 1463,
                    (2002)
                  This potential does not affect small amplitude vibrations
                  but is used in an ad hoc way to prevent the onset of
                  accidentially large amplitude fluctuations leading to
                  the occurrence of a planar conformation of the three
                  bonds i, i + 1 and i', an intermediate conformation
                  toward the chiral inversion of a methine carbon.
                  In the "Impropers" section of data file four atoms:
                  i, j, k and l are specified with i,j and l lying on the
                  backbone of the chain and k specifying the chirality
                  of j.
------------------------------------------------------------------------- */

#include "lmptype.h"
#include "mpi.h"
#include "math.h"
#include "stdlib.h"
#include "improper_ring.h"
#include "atom.h"
#include "comm.h"
#include "neighbor.h"
#include "domain.h"
#include "force.h"
#include "update.h"
#include "math_const.h"
#include "math_special.h"
#include "memory.h"
#include "error.h"

using namespace LAMMPS_NS;
using namespace MathConst;
using namespace MathSpecial;

#define TOLERANCE 0.05
#define SMALL     0.001

/* ---------------------------------------------------------------------- */

ImproperRing::ImproperRing(LAMMPS *lmp) : Improper(lmp) {}

/* ---------------------------------------------------------------------- */

ImproperRing::~ImproperRing()
{
  if (allocated) {
    memory->destroy(setflag);
    memory->destroy(k);
    memory->destroy(chi);
  }
}

/* ---------------------------------------------------------------------- */

void ImproperRing::compute(int eflag, int vflag)
{
   /* Be careful!: "chi" is the equilibrium angle in radians. */
   int i1,i2,i3,i4,n,type;

   double eimproper ;

   /* Compatibility variables. */
   double vb1x,vb1y,vb1z,vb2x,vb2y,vb2z,vb3x,vb3y,vb3z;
   double f1[3], f3[3], f4[3];

   /* Actual computation variables. */
   int at1[3], at2[3], at3[3], icomb;
   double   bvec1x[3], bvec1y[3], bvec1z[3],
            bvec2x[3], bvec2y[3], bvec2z[3],
            bvec1n[3], bvec2n[3], bend_angle[3];
   double   angle_summer, angfac, cfact1, cfact2, cfact3;
   double   cjiji, ckjji, ckjkj, fix, fiy, fiz, fjx, fjy, fjz, fkx, fky, fkz;

   eimproper = 0.0;
   if (eflag || vflag) ev_setup(eflag,vflag);
   else evflag = 0;

   /* References to simulation data. */
   double **x = atom->x;
   double **f = atom->f;
   int **improperlist = neighbor->improperlist;
   int nimproperlist = neighbor->nimproperlist;
   int nlocal = atom->nlocal;
   int newton_bond = force->newton_bond;


   /* A description of the potential can be found in
      Macromolecules 35, pp. 1463-1472 (2002). */
   for (n = 0; n < nimproperlist; n++)
   {
      /* Take the ids of the atoms contributing to the improper potential. */
      i1 = improperlist[n][0];   /* Atom "1" of Figure 1 from the above reference.*/
      i2 = improperlist[n][1];   /* Atom "2" ... */
      i3 = improperlist[n][2];   /* Atom "3" ... */
      i4 = improperlist[n][3];   /* Atom "9" ... */
      type = improperlist[n][4];

      /* Calculate the necessary variables for LAMMPS implementation.
         if (evflag) ev_tally(i1,i2,i3,i4,nlocal,newton_bond,eimproper,f1,f3,f4,
                                   vb1x,vb1y,vb1z,vb2x,vb2y,vb2z,vb3x,vb3y,vb3z);
         Although, they are irrelevant to the calculation of the potential, we keep
         them for maximal compatibility. */
      vb1x = x[i1][0] - x[i2][0]; vb1y = x[i1][1] - x[i2][1]; vb1z = x[i1][2] - x[i2][2];

      vb2x = x[i3][0] - x[i2][0]; vb2y = x[i3][1] - x[i2][1]; vb2z = x[i3][2] - x[i2][2];

      vb3x = x[i4][0] - x[i3][0]; vb3y = x[i4][1] - x[i3][1]; vb3z = x[i4][2] - x[i3][2];


      /* Pass the atom tags to form the necessary combinations. */
      at1[0] = i1; at2[0] = i2; at3[0] = i4;  /* ids: 1-2-9 */
      at1[1] = i1; at2[1] = i2; at3[1] = i3;  /* ids: 1-2-3 */
      at1[2] = i4; at2[2] = i2; at3[2] = i3;  /* ids: 9-2-3 */


      /* Initialize the sum of the angles differences. */
      angle_summer = 0.0;
      /* Take a loop over the three angles, defined by each triad: */
      for (icomb = 0; icomb < 3; icomb ++)
      {

         /* Bond vector connecting the first and the second atom. */
         bvec1x[icomb] = x[at2[icomb]][0] - x[at1[icomb]][0];
         bvec1y[icomb] = x[at2[icomb]][1] - x[at1[icomb]][1];
         bvec1z[icomb] = x[at2[icomb]][2] - x[at1[icomb]][2];
         /* also calculate the norm of the vector: */
         bvec1n[icomb] = sqrt(  bvec1x[icomb]*bvec1x[icomb]
                              + bvec1y[icomb]*bvec1y[icomb]
                              + bvec1z[icomb]*bvec1z[icomb]);
         /* Bond vector connecting the second and the third atom. */
         bvec2x[icomb] = x[at3[icomb]][0] - x[at2[icomb]][0];
         bvec2y[icomb] = x[at3[icomb]][1] - x[at2[icomb]][1];
         bvec2z[icomb] = x[at3[icomb]][2] - x[at2[icomb]][2];
         /* also calculate the norm of the vector: */
         bvec2n[icomb] = sqrt(  bvec2x[icomb]*bvec2x[icomb]
                              + bvec2y[icomb]*bvec2y[icomb]
                              + bvec2z[icomb]*bvec2z[icomb]);

         /* Calculate the bending angle of the atom triad: */
         bend_angle[icomb] = (  bvec2x[icomb]*bvec1x[icomb]
                              + bvec2y[icomb]*bvec1y[icomb]
                              + bvec2z[icomb]*bvec1z[icomb]);
         bend_angle[icomb] /= (bvec1n[icomb] * bvec2n[icomb]);
         if (bend_angle[icomb] >  1.0) bend_angle[icomb] -= SMALL;
         if (bend_angle[icomb] < -1.0) bend_angle[icomb] += SMALL;

         /* Append the current angle to the sum of angle differences. */
         angle_summer += (bend_angle[icomb] - chi[type]);
      }
      if (eflag) eimproper = (1.0/6.0) *k[type] * powint(angle_summer,6);
      /*
      printf("The tags: %d-%d-%d-%d, of type %d .\n",atom->tag[i1],atom->tag[i2],atom->tag[i3],atom->tag[i4],type);
      // printf("The coordinates of the first: %f, %f, %f.\n", x[i1][0], x[i1][1], x[i1][2]);
      // printf("The coordinates of the second: %f, %f, %f.\n", x[i2][0], x[i2][1], x[i2][2]);
      // printf("The coordinates of the third: %f, %f, %f.\n", x[i3][0], x[i3][1], x[i3][2]);
      // printf("The coordinates of the fourth: %f, %f, %f.\n", x[i4][0], x[i4][1], x[i4][2]);
      printf("The angles are: %f / %f / %f equilibrium: %f.\n", bend_angle[0], bend_angle[1], bend_angle[2],chi[type]);
      printf("The energy of the improper: %f with prefactor %f.\n", eimproper,(1.0/6.0)*k[type]);
      printf("The sum of the angles: %f.\n", angle_summer);
      */

      /* Force calculation acting on all atoms.
         Calculate the derivatives of the potential. */
      angfac = k[type] * powint(angle_summer,5);

      f1[0] = 0.0; f1[1] = 0.0; f1[2] = 0.0;
      f3[0] = 0.0; f3[1] = 0.0; f3[2] = 0.0;
      f4[0] = 0.0; f4[1] = 0.0; f4[2] = 0.0;

      /* Take a loop over the three angles, defined by each triad: */
      for (icomb = 0; icomb < 3; icomb ++)
      {
         /* Calculate the squares of the distances. */
         cjiji = bvec1n[icomb] * bvec1n[icomb];  ckjkj = bvec2n[icomb] * bvec2n[icomb];

         ckjji =   bvec2x[icomb] * bvec1x[icomb]
                 + bvec2y[icomb] * bvec1y[icomb]
                 + bvec2z[icomb] * bvec1z[icomb] ;

         cfact1 = angfac / (sqrt(ckjkj * cjiji));
         cfact2 = ckjji / ckjkj;
         cfact3 = ckjji / cjiji;

         /* Calculate the force acted on the thrid atom of the angle. */
         fkx = cfact2 * bvec2x[icomb] - bvec1x[icomb];
         fky = cfact2 * bvec2y[icomb] - bvec1y[icomb];
         fkz = cfact2 * bvec2z[icomb] - bvec1z[icomb];

         /* Calculate the force acted on the first atom of the angle. */
         fix = bvec2x[icomb] - cfact3 * bvec1x[icomb];
         fiy = bvec2y[icomb] - cfact3 * bvec1y[icomb];
         fiz = bvec2z[icomb] - cfact3 * bvec1z[icomb];

         /* Finally, calculate the force acted on the middle atom of the angle.*/
         fjx = - fix - fkx;  fjy = - fiy - fky;  fjz = - fiz - fkz;

         /* Consider the appropriate scaling of the forces: */
         fix *= cfact1; fiy *= cfact1; fiz *= cfact1;
         fjx *= cfact1; fjy *= cfact1; fjz *= cfact1;
         fkx *= cfact1; fky *= cfact1; fkz *= cfact1;

         if      (at1[icomb] == i1)  {f1[0] += fix; f1[1] += fiy; f1[2] += fiz;}
         else if (at2[icomb] == i1)  {f1[0] += fjx; f1[1] += fjy; f1[2] += fjz;}
         else if (at3[icomb] == i1)  {f1[0] += fkx; f1[1] += fky; f1[2] += fkz;}

         if      (at1[icomb] == i3)  {f3[0] += fix; f3[1] += fiy; f3[2] += fiz;}
         else if (at2[icomb] == i3)  {f3[0] += fjx; f3[1] += fjy; f3[2] += fjz;}
         else if (at3[icomb] == i3)  {f3[0] += fkx; f3[1] += fky; f3[2] += fkz;}

         if      (at1[icomb] == i4)  {f4[0] += fix; f4[1] += fiy; f4[2] += fiz;}
         else if (at2[icomb] == i4)  {f4[0] += fjx; f4[1] += fjy; f4[2] += fjz;}
         else if (at3[icomb] == i4)  {f4[0] += fkx; f4[1] += fky; f4[2] += fkz;}


         /* Store the contribution to the global arrays: */
         /* Take the id of the atom from the at1[icomb] element, i1 = at1[icomb]. */
         if (newton_bond || at1[icomb] < nlocal) {
            f[at1[icomb]][0] += fix;
            f[at1[icomb]][1] += fiy;
            f[at1[icomb]][2] += fiz;
         }
         /* Take the id of the atom from the at2[icomb] element, i2 = at2[icomb]. */
         if (newton_bond || at2[icomb] < nlocal) {
            f[at2[icomb]][0] += fjx;
            f[at2[icomb]][1] += fjy;
            f[at2[icomb]][2] += fjz;
         }
         /* Take the id of the atom from the at3[icomb] element, i3 = at3[icomb]. */
         if (newton_bond || at3[icomb] < nlocal) {
            f[at3[icomb]][0] += fkx;
            f[at3[icomb]][1] += fky;
            f[at3[icomb]][2] += fkz;
         }

      }

      if (evflag) ev_tally(i1,i2,i3,i4,nlocal,newton_bond,eimproper,f1,f3,f4,
                                   vb1x,vb1y,vb1z,vb2x,vb2y,vb2z,vb3x,vb3y,vb3z);

  }
}

/* ---------------------------------------------------------------------- */

void ImproperRing::allocate()
{
  allocated = 1;
  int n = atom->nimpropertypes;

  memory->create(k,n+1,"improper:k");
  memory->create(chi,n+1,"improper:chi");

  memory->create(setflag,n+1,"improper:setflag");
  for (int i = 1; i <= n; i++) setflag[i] = 0;
}

/* ----------------------------------------------------------------------
   set coeffs for one type
------------------------------------------------------------------------- */

void ImproperRing ::coeff(int narg, char **arg)
{
   /* Check whether there exist sufficient number of arguments.
      0: type of improper to be applied to
      1: energetic constant
      2: equilibrium angle in degrees */
   if (narg != 3) error->all(FLERR,"Incorrect args for RING improper coefficients");
   if (!allocated) allocate();

   int ilo,ihi;
   force->bounds(arg[0],atom->nimpropertypes,ilo,ihi);

   double k_one = force->numeric(arg[1]);
   double chi_one = force->numeric(arg[2]);

   int count = 0;
   for (int i = ilo; i <= ihi; i++) {
      /* Read the k parameter in kcal/mol. */
      k[i] = k_one;
      /* "chi_one" stores the equilibrium angle in degrees.
         Convert it to radians and store its cosine. */
      chi[i] = cos((chi_one/180.0)*MY_PI);
      setflag[i] = 1;
      count++;
   }

   if (count == 0) error->all(FLERR,"Incorrect args for improper coefficients");
}

/* ----------------------------------------------------------------------
   proc 0 writes out coeffs to restart file
------------------------------------------------------------------------- */

void ImproperRing ::write_restart(FILE *fp)
{
  fwrite(&k[1],sizeof(double),atom->nimpropertypes,fp);
  fwrite(&chi[1],sizeof(double),atom->nimpropertypes,fp);
}

/* ----------------------------------------------------------------------
   proc 0 reads coeffs from restart file, bcasts them
------------------------------------------------------------------------- */

void ImproperRing::read_restart(FILE *fp)
{
  allocate();

  if (comm->me == 0) {
    fread(&k[1],sizeof(double),atom->nimpropertypes,fp);
    fread(&chi[1],sizeof(double),atom->nimpropertypes,fp);
  }
  MPI_Bcast(&k[1],atom->nimpropertypes,MPI_DOUBLE,0,world);
  MPI_Bcast(&chi[1],atom->nimpropertypes,MPI_DOUBLE,0,world);

  for (int i = 1; i <= atom->nimpropertypes; i++) setflag[i] = 1;
}
