/*                                                                            */
/* CDDL HEADER START                                                          */
/*                                                                            */
/* The contents of this file are subject to the terms of the Common           */
/* Development and Distribution License Version 1.0 (the "License").          */
/*                                                                            */
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/* specific language governing permissions and limitations under the License. */
/*                                                                            */
/* When distributing Covered Code, include this CDDL HEADER in each file and  */
/* include the License file in a prominent location with the name             */
/* LICENSE.CDDL.  If applicable, add the following below this CDDL HEADER,    */
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/* identifying information:                                                   */
/*                                                                            */
/* Portions Copyright (c) [yyyy] [name of copyright owner].                   */
/* All rights reserved.                                                       */
/*                                                                            */
/* CDDL HEADER END                                                            */
/*                                                                            */

/*                                                                            */
/* Copyright (c) 2013--2014, Regents of the University of Minnesota.          */
/* All rights reserved.                                                       */
/*                                                                            */
/* Contributors:                                                              */
/*    Ryan S. Elliott                                                         */
/*    Ellad B. Tadmor                                                         */
/*    Stephen M. Whalen                                                       */
/*                                                                            */

/*                                                                            */
/* Portions Copyright (c) <FILL_year>, <FILL_copyright_holder>.               */
/* All rights reserved.                                                       */
/*                                                                            */
/* Contributors:                                                              */
/*    <FILL_name>                                                             */
/*                                                                            */

/******************************************************************************/
/*                                                                            */
/* <FILL_model_driver_name> pair potential KIM Model Driver                   */
/*                                                                            */
/* Reference: <FILL>                                                          */
/*                                                                            */
/* Language: C                                                                */
/*                                                                            */
/* Release: This file is part of the kim-api-v1.6.3 package.                  */
/*                                                                            */
/******************************************************************************/


#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include "KIM_API_C.h"
#include "KIM_API_status.h"

/******************************************************************************/
/* Below are the definitions for some constants                               */
/******************************************************************************/
#define DIM 3  /* dimensionality of space */
#define SPECCODE 1  /* internal species code */


/* Define prototype for Model Driver init */
int model_driver_init(void* km, char* paramfile_names, int* nmstrlen,
                      int* numparamfiles);

/* Define prototypes for reinit and destroy */
/* defined as static to avoid namespace clashes with other codes */
static int reinit(void* km);
static int destroy(void* km);

/* Define prototype for compute routine */
static int compute(void* km);

/* Define prototypes for pair potential calculations */
static void calc_phi(double* <FILL_parameter_1>,
                     double* <FILL_parameter_2>,
                     double* <FILL_parameter_3>,
                     double* <FILL_parameter_4>,
                     /* FILL as many parameters as needed */
                     double* cutoff, double r, double* phi);

static void calc_phi_dphi(double* <FILL_parameter_1>,
                          double* <FILL_parameter_2>,
                          double* <FILL_parameter_3>,
                          double* <FILL_parameter_4>,
                          /* FILL as many parameters as needed */
                          double* cutoff, double r, double* phi, double* dphi);

static void calc_phi_d2phi(double* <FILL_parameter_1>,
                           double* <FILL_parameter_2>,
                           double* <FILL_parameter_3>,
                           double* <FILL_parameter_4>,
                           /* FILL as many parameters as needed */
                           double* cutoff, double r, double* phi, double* dphi,
                           double* d2phi);

/* Define model_buffer structure */
struct model_buffer
{
  int NBC;
  int HalfOrFull;
  int IterOrLoca;
  int energy_ind;
  int forces_ind;
  int particleEnergy_ind;
  int process_dEdr_ind;
  int process_d2Edr2_ind;
  int model_index_shift;
  int numberOfParticles_ind;
  int particleSpecies_ind;
  int coordinates_ind;
  int numberContribParticles_ind;
  int boxSideLengths_ind;
  int get_neigh_ind;
  int cutoff_ind;

  double Pcutoff;
  double cutsq;
  double <FILL_parameter_1>;
  double <FILL_parameter_2>;
  double <FILL_parameter_3>;
  double <FILL_parameter_4>;
  /* FILL as many parameters as needed */
};


/* Calculate pair potential phi(r) */
static void calc_phi(double* <FILL_parameter_1>,
                     double* <FILL_parameter_2>,
                     double* <FILL_parameter_3>,
                     double* <FILL_parameter_4>,
                     /* FILL as many parameters as needed */
                     double* cutoff, double r, double* phi)
{
  /* local variables */
  /* FILL: place any local variable definitions here */

  if (r > *cutoff)
  {
    /* Argument exceeds cutoff radius */
    *phi = 0.0;
  }
  else
  {
    *phi = <FILL_functional_form_of_phi(r)>;
  }

  return;
}

/* Calculate pair potential phi(r) and its derivative dphi(r) */
static void calc_phi_dphi(double* <FILL_parameter_1>,
                          double* <FILL_parameter_2>,
                          double* <FILL_parameter_3>,
                          double* <FILL_parameter_4>,
                          /* FILL as many parameters as needed */
                          double* cutoff, double r, double* phi, double* dphi)
{
  /* local variables */
  /* FILL: place any local variable definitions here */

  if (r > *cutoff)
  {
    /* Argument exceeds cutoff radius */
    *phi = 0.0;
    *dphi = 0.0;
  }
  else
  {
    *phi = <FILL functional form of phi(r)>;
    *dphi = <FILL functional form of dphi(r)>;
  }

  return;
}

/* Calculate pair potential phi(r) and its 1st & 2nd derivatives dphi(r), */
/* d2phi(r) */
static void calc_phi_d2phi(double* <FILL_parameter_1>,
                           double* <FILL_parameter_2>,
                           double* <FILL_parameter_3>,
                           double* <FILL_parameter_4>,
                           /* FILL as many parameters as needed */
                           double* cutoff, double r, double* phi, double* dphi,
                           double* d2phi)
{
  /* local variables */
  /* FILL: place any local variable definitions here */

  if (r > *cutoff)
  {
    /* Argument exceeds cutoff radius */
    *phi = 0.0;
    *dphi = 0.0;
    *d2phi = 0.0;
  }
  else
  {
    *phi = <FILL functional form of phi(r)>;
    *dphi = <FILL functional form of dphi(r)>;
    *d2phi = <FILL functional form of d2phi(r)>;
  }

  return;
}

/* compute function */
static int compute(void* km)
{
  /* local variables */
  intptr_t* pkim = *((intptr_t**) km);
  double R;
  double R_pairs[2];
  double *pR_pairs = &(R_pairs[0]);
  double Rsqij;
  double phi;
  double dphi;
  double d2phi;
  double dEidr;
  double d2Eidr;
  double Rij[DIM];
  double *pRij = &(Rij[0]);
  double Rij_pairs[2][3];
  double *pRij_pairs = &(Rij_pairs[0][0]);
  int ier;
  int i;
  int i_pairs[2];
  int *pi_pairs = &(i_pairs[0]);
  int j;
  int j_pairs[2];
  int *pj_pairs = &(j_pairs[0]);
  int jj;
  int k;
  int currentPart;
  int* neighListOfCurrentPart;
  struct model_buffer* buffer;
  int comp_energy;
  int comp_force;
  int comp_particleEnergy;
  int comp_process_dEdr;
  int comp_process_d2Edr2;
  int NBC;
  int HalfOrFull;
  int IterOrLoca;
  int model_index_shift;
  int zero = 0;
  int one = 1;
  int request;

  int* nParts;
  int* particleSpecies;
  double* cutoff;
  double* cutsq;
  double* <FILL_parameter_1>;
  double* <FILL_parameter_2>;
  double* <FILL_parameter_3>;
  double* <FILL_parameter_4>;
  /* FILL as many parameters as needed */
  double* Rij_list;
  double* coords;
  double* energy;
  double* force;
  double* particleEnergy;
  double* boxSideLengths;
  int* numContrib;
  int numberContrib;
  int numOfPartNeigh;
  typedef int (*get_neigh_ptr)(void *,int *,int *,int *, int *, int **,
                               double **);
  get_neigh_ptr get_neigh = NULL;

  /* get buffer from KIM object */
  buffer = (struct model_buffer*) KIM_API_get_model_buffer(pkim, &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_get_model_buffer", ier);
    return ier;
  }

  /* unpack info from the buffer */
  NBC = buffer->NBC;
  HalfOrFull = buffer->HalfOrFull;
  IterOrLoca = buffer->IterOrLoca;
  model_index_shift = buffer->model_index_shift;
  cutsq = &(buffer->cutsq);
  <FILL_parameter_1> = &(buffer-><FILL_parameter_1>);
  <FILL_parameter_2> = &(buffer-><FILL_parameter_2>);
  <FILL_parameter_3> = &(buffer-><FILL_parameter_3>);
  <FILL_parameter_4> = &(buffer-><FILL_parameter_4>);
  /* also FILL additional parameters here if there are any ... */

  /* check to see if we have been asked to compute the forces, */
  /* particleEnergy, and d1Edr */
  KIM_API_getm_compute_by_index(
      pkim, &ier, 5*3,
      buffer->energy_ind,         &comp_energy,         1,
      buffer->forces_ind,         &comp_force,          1,
      buffer->particleEnergy_ind, &comp_particleEnergy, 1,
      buffer->process_dEdr_ind,   &comp_process_dEdr,   1,
      buffer->process_d2Edr2_ind, &comp_process_d2Edr2, 1);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__,
                         "KIM_API_getm_compute_by_index", ier);
    return ier;
  }

  KIM_API_getm_data_by_index(
      pkim, &ier, 9*3,
      buffer->cutoff_ind,                 &cutoff,         1,
      buffer->numberOfParticles_ind,      &nParts,         1,
      buffer->particleSpecies_ind,        &particleSpecies,1,
      buffer->coordinates_ind,            &coords,         1,
      buffer->numberContribParticles_ind, &numContrib,     (HalfOrFull==1),
      buffer->boxSideLengths_ind,         &boxSideLengths, (NBC==2),
      buffer->energy_ind,                 &energy,         comp_energy,
      buffer->forces_ind,                 &force,          comp_force,
      buffer->particleEnergy_ind,         &particleEnergy, comp_particleEnergy);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_getm_data_by_index", ier);
    return ier;
  }
  if (NBC!=3)
  {
    get_neigh = (get_neigh_ptr)
        KIM_API_get_method_by_index(pkim, buffer->get_neigh_ind, &ier);
    if (KIM_STATUS_OK > ier)
    {
      KIM_API_report_error(__LINE__, __FILE__,
                           "KIM_API_get_method_by_index", ier);
      return ier;
    }
  }

  if (HalfOrFull == 1)
  {
    if (3 != NBC)
    {
      /* non-CLUSTER cases */
      numberContrib = *numContrib;
    }
    else
    {
      /* CLUSTER cases */
      numberContrib = *nParts;
    }
  }
  else
  {
    /* provide initialization even if not used */
    numberContrib = *nParts;
  }

  /* Check to be sure that the species are correct */
  /**/
  ier = KIM_STATUS_FAIL; /* assume an error */
  for (i = 0; i < *nParts; ++i)
  {
    if ( SPECCODE != particleSpecies[i])
    {
      KIM_API_report_error(__LINE__, __FILE__,
                           "Unexpected species detected", ier);
      return ier;
    }
  }
  ier = KIM_STATUS_OK;  /* everything is ok */

  /* initialize potential energies, forces, and virial term */
  if (comp_particleEnergy)
  {
    for (i = 0; i < *nParts; ++i)
    {
      particleEnergy[i] = 0.0;
    }
  }
  if (comp_energy)
  {
    *energy = 0.0;
  }

  if (comp_force)
  {
    for (i = 0; i < *nParts; ++i)
    {
      for (k = 0; k < DIM; ++k)
      {
        force[i*DIM + k] = 0.0;
      }
    }
  }

  /* Initialize neighbor handling for CLUSTER NBC */
  if (3 == NBC)
  {
    /* CLUSTER */
    neighListOfCurrentPart = (int *) malloc((*nParts)*sizeof(int));
  }

  /* Initialize neighbor handling for Iterator mode */

  if (1 == IterOrLoca)
  {
    ier = (*get_neigh)(&pkim, &zero, &zero, &currentPart, &numOfPartNeigh,
                       &neighListOfCurrentPart, &Rij_list);
    /* check for successful initialization */
    if (KIM_STATUS_NEIGH_ITER_INIT_OK != ier)
    {
      KIM_API_report_error(__LINE__, __FILE__, "KIM_API_get_neigh", ier);
      ier = KIM_STATUS_FAIL;
      return ier;
    }
  }

  /* Compute energy and forces */

  /* loop over particles and compute enregy and forces */
  i = -1;
  while( 1 )
  {
    /* Set up neighbor list for next part for all NBC methods */
    if (1 == IterOrLoca)
    {
      /* ITERATOR mode */
      ier = (*get_neigh)(&pkim, &zero, &one, &currentPart, &numOfPartNeigh,
                         &neighListOfCurrentPart, &Rij_list);
      if (KIM_STATUS_NEIGH_ITER_PAST_END == ier)
      {
        /* the end of the list, terminate loop */
        break;
      }
      if (KIM_STATUS_OK > ier)
      {
        /* some sort of problem, exit */
        KIM_API_report_error(__LINE__, __FILE__, "KIM_API_get_neigh", ier);
        return ier;
      }

      i = currentPart + model_index_shift;
    }
    else
    {
      i++;
      if (*nParts <= i)
      {
        /* incremented past end of list, terminate loop */
        break;
      }

      if (3 == NBC)
      {
        /* CLUSTER NBC method */
        numOfPartNeigh = *nParts - (i + 1);
        for (k = 0; k < numOfPartNeigh; ++k)
        {
          neighListOfCurrentPart[k] = i + k + 1 - model_index_shift;
        }
        ier = KIM_STATUS_OK;
      }
      else
      {
        request = i - model_index_shift;
        ier = (*get_neigh)(&pkim, &one, &request,
                           &currentPart, &numOfPartNeigh,
                           &neighListOfCurrentPart, &Rij_list);
        if (KIM_STATUS_OK != ier)
        {
          /* some sort of problem, exit */
          KIM_API_report_error(__LINE__, __FILE__, "KIM_API_get_neigh", ier);
          ier = KIM_STATUS_FAIL;
          return ier;
        }
      }
    }

    /* loop over the neighbors of particle i */
    for (jj = 0; jj < numOfPartNeigh; ++ jj)
    {
      j = neighListOfCurrentPart[jj] + model_index_shift;  /* get neighbor ID */

      /* compute relative position vector and squared distance */
      Rsqij = 0.0;
      for (k = 0; k < DIM; ++k)
      {
        if (0 != NBC)
        {
          /* all methods except NEIGH_RVEC */
          Rij[k] = coords[j*DIM + k] - coords[i*DIM + k];
        }
        else
        {
          /* NEIGH_RVEC_* methods */
          Rij[k] = Rij_list[jj*DIM + k];
        }

        /* apply periodic boundary conditions if required */
        if (2 == NBC)
        {
          if (abs(Rij[k]) > 0.5*boxSideLengths[k])
          {
            Rij[k] -= (Rij[k]/fabs(Rij[k]))*boxSideLengths[k];
          }
        }

        /* compute squared distance */
        Rsqij += Rij[k]*Rij[k];
      }

      /* compute energy and force */
      if (Rsqij < *cutsq)
      {
        /* particles are interacting ? */
        R = sqrt(Rsqij);
        if (comp_process_d2Edr2)
        {
          /* compute pair potential and its derivatives */
          calc_phi_d2phi(<FILL_parameter_1>,
                         <FILL_parameter_2>,
                         <FILL_parameter_3>,
                         <FILL_parameter_4>,
                         /* FILL as many parameters as needed */
                         cutoff, R, &phi, &dphi, &d2phi);

          /* compute dEidr */
          if ((1 == HalfOrFull) && (j < numberContrib))
          {
            /* Half mode -- double contribution */
            dEidr = dphi;
            d2Eidr = d2phi;
          }
          else
          {
            /* Full mode -- regular contribution */
            dEidr = 0.5*dphi;
            d2Eidr = 0.5*d2phi;
          }
        }
        else if (comp_force || comp_process_dEdr)
        {
          /* compute pair potential and its derivative */
          calc_phi_dphi(<FILL_parameter_1>,
                        <FILL_parameter_2>,
                        <FILL_parameter_3>,
                        <FILL_parameter_4>,
                        /* FILL as many parameters as needed */
                        cutoff, R, &phi, &dphi);

          /* compute dEidr */
          if ((1 == HalfOrFull) && (j < numberContrib))
          {
            /* Half mode -- double contribution */
            dEidr = dphi;
          }
          else
          {
            /* Full mode -- regular contribution */
            dEidr = 0.5*dphi;
          }
        }
        else
        {
          /* compute just pair potential */
          calc_phi(<FILL_parameter_1>,
                   <FILL_parameter_2>,
                   <FILL_parameter_3>,
                   <FILL_parameter_4>,
                   /* FILL as many parameters as needed */
                   cutoff, R, &phi);
        }

        /* contribution to energy */
        if (comp_particleEnergy)
        {
          particleEnergy[i] += 0.5*phi;
          /* if half list add energy for the other particle in the pair */
          if ((1 == HalfOrFull) && (j < numberContrib))
          {
            particleEnergy[j] += 0.5*phi;
          }
        }
        if (comp_energy)
        {
          if ((1 == HalfOrFull) && (j < numberContrib))
          {
            /* Half mode -- add v to total energy */
            *energy += phi;
          }
          else
          {
            /* Full mode -- add half v to total energy */
            *energy += 0.5*phi;
          }
        }

        /* contribution to process_dEdr */
        if (comp_process_dEdr)
        {
          ier = KIM_API_process_dEdr(km, &dEidr, &R, &pRij, &i, &j);
        }

        /* contribution to process_d2Edr2 */
        if (comp_process_d2Edr2)
        {
          R_pairs[0] = R_pairs[1] = R;
          Rij_pairs[0][0] = Rij_pairs[1][0] = Rij[0];
          Rij_pairs[0][1] = Rij_pairs[1][1] = Rij[1];
          Rij_pairs[0][2] = Rij_pairs[1][2] = Rij[2];
          i_pairs[0] = i_pairs[1] = i;
          j_pairs[0] = j_pairs[1] = j;

          ier = KIM_API_process_d2Edr2(km, &d2Eidr, &pR_pairs, &pRij_pairs,
                                       &pi_pairs, &pj_pairs);
        }

        /* contribution to forces */
        if (comp_force)
        {
          for (k = 0; k < DIM; ++k)
          {
            force[i*DIM + k] += dEidr*Rij[k]/R;  /* accumulate force on i */
            force[j*DIM + k] -= dEidr*Rij[k]/R;  /* accumulate force on j */
          }
        }
      }
    }  /* loop on jj */
  }  /* infinite while loop (terminated by break statements above) */

  /* Free temporary storage */
  if (3 == NBC)
  {
    free(neighListOfCurrentPart);
  }

  /* everything is great */
  ier = KIM_STATUS_OK;

  return ier;
}

/* Initialization function */
int model_driver_init(void *km, char* paramfile_names, int* nmstrlen,
                      int* numparamfiles)
{
  /* KIM variables */
  intptr_t* pkim = *((intptr_t**) km);
  char* paramfile1name;
  char* paramfile2name;
  <FILL as many file name pointers as needed>

  /* Local variables */
  FILE* fid;
  double cutoff;
  double <FILL_parameter_1>;
  double <FILL_parameter_2>;
  double <FILL_parameter_3>;
  double <FILL_parameter_4>;
  /* FILL as many parameters as needed */
  double* model_cutoff;
  int ier;
  struct model_buffer* buffer;
  const char* NBCstr;

  /* set paramfile1name */
  if (*numparamfiles != 1)
  {
    ier = KIM_STATUS_FAIL;
    KIM_API_report_error(__LINE__, __FILE__,
                         "Incorrect number of parameter files.", ier);
    return ier;
  }
  paramfile1name = paramfile_names;
  paramfile2name = &(paramfile_names[1*(*nmstrlen)]);
  <FILL as many file name pointers as needed>

  /* store pointer to functions in KIM object */
  KIM_API_setm_method(pkim, &ier, 3*4,
                      "compute", 1, &compute, 1,
                      "reinit",  1, &reinit,  1,
                      "destroy", 1, &destroy, 1);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_setm_data", ier);
    return ier;
  }

  /* Read in model parameters from parameter file */
  fid = fopen(paramfile1name, "r");
  if (fid == NULL)
  {
    ier = KIM_STATUS_FAIL;
    KIM_API_report_error(
        __LINE__, __FILE__,
        "Unable to open parameter file for Morse parameters", ier);
    return ier;
  }

  ier = fscanf(fid, "%lf \n%lf \n%lf \n%lf",
               &cutoff,  /* cutoff distance in angstroms */
               &<FILL_parameter_1>,
               &<FILL_parameter_2>,
               &<FILL_parameter_3>,
               &<FILL_parameter_4>,
               /* FILL as many parameters as needed */
               );
  fclose(fid);

  /* check that we read the right number of parameters */
  if (<FILL_number_of_parameters> != ier)
  {
    ier = KIM_STATUS_FAIL;
    KIM_API_report_error(__LINE__, __FILE__,
                         "Unable to read all parameters", ier);
    return ier;
  }

  /* FILL process the remaining parameter files */

  /* convert to appropriate units */
  cutoff *= KIM_API_convert_to_act_unit(pkim, "A", "eV", "e", "K", "ps",
                                        1.0, 0.0,  0.0, 0.0, 0.0, &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__,
                         "KIM_API_convert_to_act_unit", ier);
    return ier;
  }

  <FILL_parameter_1> *= KIM_API_convert_to_act_unit(
      pkim, "A", "eV", "e", "K", "ps",
      <FILL exponents (5) for parameter 1>, &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__,
                         "KIM_API_convert_to_act_unit", ier);
    return ier;
  }

  <FILL_parameter_2> *= KIM_API_convert_to_act_unit(
      pkim, "A", "eV", "e", "K", "ps",
      <FILL exponents (5) for parameter 2>, &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__,
                         "KIM_API_convert_to_act_unit", ier);
    return ier;
  }

  <FILL_parameter_3> *= KIM_API_convert_to_act_unit(
      pkim, "A", "eV", "e", "K", "ps",
      <FILL exponents (5) for parameter 3>, &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__,
                         "KIM_API_convert_to_act_unit", ier);
    return ier;
  }

  <FILL_parameter_4> *= KIM_API_convert_to_act_unit(
      pkim, "A", "eV", "e", "K", "ps",
      <FILL exponents (5) for parameter 4>, &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__,
                         "KIM_API_convert_to_act_unit", ier);
    return ier;
  }

  /* FILL as many parameters as necessary */

  /* store model cutoff in KIM object */
  model_cutoff = (double*) KIM_API_get_data(pkim, "cutoff", &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_get_data", ier);
    return ier;
  }
  *model_cutoff = cutoff;

  /* allocate buffer */
  buffer = (struct model_buffer*) malloc(sizeof(struct model_buffer));
  if (NULL == buffer)
  {
    ier = KIM_STATUS_FAIL;
    KIM_API_report_error(__LINE__, __FILE__, "malloc", ier);
    return ier;
  }

  /* setup buffer */
  /* set value of parameters */
  buffer->Pcutoff = *model_cutoff;
  buffer->cutsq = (*model_cutoff)*(*model_cutoff);
  buffer-><FILL_parameter_1> = <FILL_parameter_1>;
  buffer-><FILL_parameter_2> = <FILL_parameter_2>;
  buffer-><FILL_parameter_3> = <FILL_parameter_3>;
  buffer-><FILL_parameter_4> = <FILL_parameter_4>;
  /* FILL as many parameters as needed */

  /* Determine neighbor list boundary condition (NBC) */
  ier = KIM_API_get_NBC_method(pkim, &NBCstr);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_get_NBC_method", ier);
    return ier;
  }
  if ((!strcmp("NEIGH_RVEC_H",NBCstr)) || (!strcmp("NEIGH_RVEC_F",NBCstr)))
  {
    buffer->NBC = 0;
  }
  else if ((!strcmp("NEIGH_PURE_H",NBCstr)) || (!strcmp("NEIGH_PURE_F",NBCstr)))
  {
    buffer->NBC = 1;
  }
  else if ((!strcmp("MI_OPBC_H",NBCstr)) || (!strcmp("MI_OPBC_F",NBCstr)))
  {
    buffer->NBC = 2;
  }
  else if (!strcmp("CLUSTER",NBCstr))
  {
    buffer->NBC = 3;
  }
  else
  {
    ier = KIM_STATUS_FAIL;
    KIM_API_report_error(__LINE__, __FILE__, "Unknown NBC method", ier);
    return ier;
  }

  /* Determine if Half or Full neighbor lists are being used */
  /*****************************/
  /* HalfOrFull = 1 -- Half    */
  /*            = 2 -- Full    */
  /*****************************/
  if (KIM_API_is_half_neighbors(pkim, &ier))
  {
    buffer->HalfOrFull = 1;
  }
  else
  {
    buffer->HalfOrFull = 2;
  }

  /* determine neighbor list handling mode */
  if (buffer->NBC != 3)
  {
    /******************************/
    /* IterOrLoca = 1 -- Iterator */
    /*            = 2 -- Locator  */
    /******************************/
    buffer->IterOrLoca = KIM_API_get_neigh_mode(pkim, &ier);
    if (KIM_STATUS_OK > ier)
    {
      KIM_API_report_error(__LINE__, __FILE__, "KIM_API_get_neigh_mode", ier);
      return ier;
    }
    if ((buffer->IterOrLoca != 1) && (buffer->IterOrLoca != 2))
    {
      ier = KIM_STATUS_FAIL;
      KIM_API_report_error(__LINE__, __FILE__,
                           "Unsupported IterOrLoca mode", ier);
      return ier;
    }
  }
  else
  {
    buffer->IterOrLoca = 2;  /* for CLUSTER NBC */
  }

  buffer->model_index_shift = KIM_API_get_model_index_shift(pkim);

  KIM_API_getm_index(
      pkim, &ier, 12*3,
      "cutoff",                      &(buffer->cutoff_ind),                 1,
      "numberOfParticles",           &(buffer->numberOfParticles_ind),      1,
      "particleSpecies",             &(buffer->particleSpecies_ind),        1,
      "numberContributingParticles", &(buffer->numberContribParticles_ind), 1,
      "coordinates",                 &(buffer->coordinates_ind),            1,
      "get_neigh",                   &(buffer->get_neigh_ind),              1,
      "boxSideLengths",              &(buffer->boxSideLengths_ind),         1,
      "energy",                      &(buffer->energy_ind),                 1,
      "forces",                      &(buffer->forces_ind),                 1,
      "particleEnergy",              &(buffer->particleEnergy_ind),         1,
      "process_dEdr",                &(buffer->process_dEdr_ind),           1,
      "process_d2Edr2",              &(buffer->process_d2Edr2_ind),         1
                     );
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_getm_index", ier);
    return ier;
  }
  /* end setup buffer */

  /* store in model buffer */
  KIM_API_set_model_buffer(pkim, (void*) buffer, &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_set_model_buffer", ier);
    return ier;
  }

  /* set pointers to parameters in KIM object */
  KIM_API_setm_data(
      pkim, &ier, <FILL_number_of_parameters_plus_two>*4,
      "PARAM_FREE_cutoff", 1, &(buffer->Pcutoff), 1,
      "PARAM_FIXED_cutsq", 1, &(buffer->cutsq), 1,
      "<FILL_parameter_type_parameter_1>", 1, &(buffer-><FILL_parameter_1>), 1,
      "<FILL_parameter_type_parameter_2>", 1, &(buffer-><FILL_parameter_2>), 1,
      "<FILL_parameter_type_parameter_3>", 1, &(buffer-><FILL_parameter_3>), 1,
      "<FILL_parameter_type_parameter_4>", 1, &(buffer-><FILL_parameter_4>), 1
      /* FILL as many parameters as needed */
                    );
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_setm_data", ier);
    return ier;
  }

  return KIM_STATUS_OK;
}

/* Reinitialization function */
static int reinit(void *km)
{
  /* Local variables */
  intptr_t* pkim = *((intptr_t**) km);
  int ier;
  double *cutoff;
  struct model_buffer* buffer;

  /* get buffer from KIM object */
  buffer = (struct model_buffer*) KIM_API_get_model_buffer(pkim, &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_get_model_buffer", ier);
    return ier;
  }

  /* set new values in KIM object     */
  /*                                  */
  /* store model cutoff in KIM object */
  cutoff = KIM_API_get_data(pkim, "cutoff", &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_get_data", ier);
    return ier;
  }
  *cutoff = buffer->Pcutoff;

  /* set value of parameter cutsq */
  buffer->cutsq = (*cutoff)*(*cutoff);

  /* FILL: recompute any FIXED parameters that need to be */

  ier = KIM_STATUS_OK;
  return ier;
}

/* destroy function */
static int destroy(void *km)
{
  /* Local variables */
  intptr_t* pkim = *((intptr_t**) km);
  struct model_buffer* buffer;
  int ier;

  /* get model buffer from KIM object */
  buffer = (struct model_buffer*) KIM_API_get_model_buffer(pkim, &ier);
  if (KIM_STATUS_OK > ier)
  {
    KIM_API_report_error(__LINE__, __FILE__, "KIM_API_get_model_buffer", ier);
    return ier;
  }

  /* free the buffer */
  free(buffer);

  ier = KIM_STATUS_OK;
  return ier;
}
