git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@14082 f3b2605a-c512-4ea7-a41b-209d697bcdaa

src/compute_rdf.cpp

@@ -95,7 +95,6 @@ ComputeRDF::ComputeRDF(LAMMPS *lmp, int narg, char **arg) :
   typecount = new int[ntypes+1];
   icount = new int[npairs];
   jcount = new int[npairs];
-  duplicates = new int[npairs];
 }
 
 /* ---------------------------------------------------------------------- */
@@ -114,14 +113,13 @@ ComputeRDF::~ComputeRDF()
   delete [] typecount;
   delete [] icount;
   delete [] jcount;
-  delete [] duplicates;
 }
 
 /* ---------------------------------------------------------------------- */
 
 void ComputeRDF::init()
 {
-  int i,j,m;
+  int i,m;
 
   if (force->pair) delr = force->pair->cutforce / nbin;
   else error->all(FLERR,"Compute rdf requires a pair style be defined");
@@ -145,17 +143,12 @@ void ComputeRDF::init()
 
   // icount = # of I atoms participating in I,J pairs for each histogram
   // jcount = # of J atoms participating in I,J pairs for each histogram
-  // duplicates = # of atoms in both groups I and J for each histogram
 
   for (m = 0; m < npairs; m++) {
     icount[m] = 0;
     for (i = ilo[m]; i <= ihi[m]; i++) icount[m] += typecount[i];
     jcount[m] = 0;
     for (i = jlo[m]; i <= jhi[m]; i++) jcount[m] += typecount[i];
-    duplicates[m] = 0;
-    for (i = ilo[m]; i <= ihi[m]; i++)
-      for (j = jlo[m]; j <= jhi[m]; j++)
-        if (i == j) duplicates[m] += typecount[i];
   }
 
   int *scratch = new int[npairs];
@@ -163,11 +156,10 @@ void ComputeRDF::init()
   for (i = 0; i < npairs; i++) icount[i] = scratch[i];
   MPI_Allreduce(jcount,scratch,npairs,MPI_INT,MPI_SUM,world);
   for (i = 0; i < npairs; i++) jcount[i] = scratch[i];
-  MPI_Allreduce(duplicates,scratch,npairs,MPI_INT,MPI_SUM,world);
-  for (i = 0; i < npairs; i++) duplicates[i] = scratch[i];
   delete [] scratch;
 
   // need an occasional half neighbor list
+
   int irequest = neighbor->request(this,instance_me);
   neighbor->requests[irequest]->pair = 0;
   neighbor->requests[irequest]->compute = 1;
@@ -273,12 +265,10 @@ void ComputeRDF::compute_array()
   MPI_Allreduce(hist[0],histall[0],npairs*nbin,MPI_DOUBLE,MPI_SUM,world);
 
   // convert counts to g(r) and coord(r) and copy into output array
-  // vfrac = fraction of volume in shell m
-  // npairs = number of pairs, corrected for duplicates
-  // duplicates = pairs in which both atoms are the same
+  // nideal = # of J atoms surrounding single I atom in a single bin
+  //   assuming J atoms are at uniform density
 
-  double constant,vfrac,gr,ncoord,rlower,rupper;
-  int pairtot;
+  double constant,nideal,gr,ncoord,rlower,rupper;
 
   if (domain->dimension == 3) {
     constant = 4.0*MY_PI / (3.0*domain->xprd*domain->yprd*domain->zprd);
@@ -288,13 +278,12 @@ void ComputeRDF::compute_array()
       for (ibin = 0; ibin < nbin; ibin++) {
         rlower = ibin*delr;
         rupper = (ibin+1)*delr;
-        vfrac = constant * (rupper*rupper*rupper - rlower*rlower*rlower);
-        pairtot = icount[m] * jcount[m] - duplicates[m];
-        if (vfrac * pairtot != 0.0)
-          gr = histall[m][ibin] / (vfrac * pairtot);
+        nideal = constant *
+          (rupper*rupper*rupper - rlower*rlower*rlower) * jcount[m];
+        if (icount[m]*nideal != 0.0)
+          gr = histall[m][ibin] / (icount[m]*nideal);
         else gr = 0.0;
-        if (icount[m] != 0)
-          ncoord += gr * vfrac * pairtot / icount[m];
+        ncoord += gr*nideal;
         array[ibin][1+2*m] = gr;
         array[ibin][2+2*m] = ncoord;
       }
@@ -308,13 +297,11 @@ void ComputeRDF::compute_array()
       for (ibin = 0; ibin < nbin; ibin++) {
         rlower = ibin*delr;
         rupper = (ibin+1)*delr;
-        vfrac = constant * (rupper*rupper - rlower*rlower);
-        pairtot = icount[m] * jcount[m] - duplicates[m];
-        if (vfrac * pairtot != 0.0)
-          gr = histall[m][ibin] / (vfrac * pairtot);
+        nideal = constant * (rupper*rupper - rlower*rlower) * jcount[m];
+        if (icount[m]*nideal != 0.0)
+          gr = histall[m][ibin] / (icount[m]*nideal);
         else gr = 0.0;
-        if (icount[m] != 0)
-          ncoord += gr * vfrac * pairtot / icount[m];
+        ncoord += gr*nideal;
         array[ibin][1+2*m] = gr;
         array[ibin][2+2*m] = ncoord;
       }

src/compute_rdf.h

@@ -44,7 +44,7 @@ class ComputeRDF : public Compute {
   double **histall;      // summed histogram bins across all procs
 
   int *typecount;
-  int *icount,*jcount,*duplicates;
+  int *icount,*jcount;
 
   class NeighList *list; // half neighbor list
 };