TABLE OF CONTENTS

1. QMD-MGDFT/minimage.c

QMD-MGDFT/minimage.c

   Ab initio real space code with multigrid acceleration
   Quantum molecular dynamics package.
   Version: 2.1.5

   Copyright (C) 1995  Emil Briggs
   Copyright (C) 1998  Emil Briggs, Charles Brabec, Mark Wensell, 
                       Dan Sullivan, Chris Rapcewicz, Jerzy Bernholc
   Copyright (C) 2001  Emil Briggs, Wenchang Lu,
                       Marco Buongiorno Nardelli,Charles Brabec, 
                       Mark Wensell,Dan Sullivan, Chris Rapcewicz,
                       Jerzy Bernholc

   REAL minimage(ION *ip1, ION *ip2, REAL *xtal_r)
   This function returns the minimum distance between two ions in the
   supercell. It also returns the x, y, and z coordinates for the minimum
   distance. 

   ip1, ip2: point to structure ION, only use the coordinates

   return the minimum distance
   xtal_r: store the shortest vector 

   get _te.c iiforce.c

   metric.c

    #include "md.h"
    #include <float.h>
    #include <math.h>
    
    
    REAL minimage(ION *ip1, ION *ip2, REAL *xtal_r)
    {
    
        int ix, iy, iz, idx, idxmin=0;
        REAL r[27], ax[3], rmin, x[27], y[27], z[27];
    
    
    
        /* If cluster boundary conditions just compute r and return */
        if(ct.boundaryflag == CLUSTER) {
    
          xtal_r[0] = ip1->xtal[0] - ip2->xtal[0];
          xtal_r[1] = ip1->xtal[1] - ip2->xtal[1];
          xtal_r[2] = ip1->xtal[2] - ip2->xtal[2];
    
          return metric(xtal_r);
    
        } /* end if */
    
      
        /* Loop over all possible combinations and generate r */
    
        idx = 0;
        for(ix = -1;ix <= 1;ix++) {
          
          for(iy = -1;iy <= 1;iy++) {
            
            for(iz = -1;iz <= 1;iz++) {
              
              x[idx] = ip1->xtal[0] - ip2->xtal[0] + (REAL)ix; 
              y[idx] = ip1->xtal[1] - ip2->xtal[1] + (REAL)iy;
              z[idx] = ip1->xtal[2] - ip2->xtal[2] + (REAL)iz;
              if(ct.boundaryflag == SURFACE) {
    
                z[idx] = ip1->xtal[2] - ip2->xtal[2];
    
              } /* end if */
    
              ax[0] = x[idx];
              ax[1] = y[idx];
              ax[2] = z[idx];
    
              r[idx] = metric(ax);
                    
              idx++;
              
            } /* end for ix */
            
          } /* end for iy */
          
        } /* end for iz */
    
    
        /* Next we find rmin */
        rmin = 100000.0;
        for(idx = 0;idx < 27;idx++) {
    
            /* Gaurd against roundoff */
            if( (r[idx] > 1.0e-5) && (r[idx] < rmin) ) {
    
                rmin = r[idx];
                idxmin = idx;
    
            } /* end if */
    
        } /* end for */
    
    
        xtal_r[0] = x[idxmin];
        xtal_r[1] = y[idxmin];
        xtal_r[2] = z[idxmin];
    
        return rmin;
    
    } /* end minimage */