diff --git a/src/MISC/fix_imd.cpp b/src/MISC/fix_imd.cpp
index 9192f8a24c..6f2bb53a8c 100644
--- a/src/MISC/fix_imd.cpp
+++ b/src/MISC/fix_imd.cpp
@@ -76,7 +76,6 @@ negotiate an appropriate license for such distribution."
 #endif
 
 #include <cerrno>
-#include <vector>
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -461,7 +460,6 @@ MPI_Datatype MPI_CommData;
 FixIMD::FixIMD(LAMMPS *lmp, int narg, char **arg) :
   Fix(lmp, narg, arg)
 {
-
   if (narg < 4)
     error->all(FLERR,"Illegal fix imd command");
 
@@ -508,7 +506,9 @@ FixIMD::FixIMD(LAMMPS *lmp, int narg, char **arg) :
       vel_flag = utils::logical(FLERR, arg[iarg+1], false, lmp);
     } else if (0 == strcmp(arg[iarg], "forces")) {
       force_flag = utils::logical(FLERR, arg[iarg+1], false, lmp);
-    } else error->all(FLERR,"Unknown fix imd parameter");
+    } else {
+      error->all(FLERR,"Unknown fix imd parameter");
+    }
     ++iarg; ++iarg;
   }
 
@@ -542,7 +542,6 @@ FixIMD::FixIMD(LAMMPS *lmp, int narg, char **arg) :
     imdsinfo->energies = false;
   }
 
-
   bigint n = group->count(igroup);
   if (n > MAXSMALLINT) error->all(FLERR,"Too many atoms for fix imd");
   num_coords = static_cast<int> (n);
@@ -568,25 +567,30 @@ FixIMD::FixIMD(LAMMPS *lmp, int narg, char **arg) :
   idmap = nullptr;
   rev_idmap = nullptr;
 
+  if (imd_version == 3) {
+    msglen = 0;
+    if (imdsinfo->time) {
+      msglen += 24+IMDHEADERSIZE;
+    }
+    if (imdsinfo->box) {
+      msglen += 9*4+IMDHEADERSIZE;
+    }
+    if (imdsinfo->coords) {
+      msglen += 3*4*num_coords+IMDHEADERSIZE;
+    }
+    if (imdsinfo->velocities) {
+      msglen += 3*4*num_coords+IMDHEADERSIZE;
+    }
+    if (imdsinfo->forces) {
+      msglen += 3*4*num_coords+IMDHEADERSIZE;
+    }
+    msgdata = new char[msglen];
+  }
+  else {
+    msglen = 3*sizeof(float)*num_coords+IMDHEADERSIZE;
+    msgdata = new char[msglen];
+  }
   
-  msglen = 0;
-  if (imdsinfo->time) {
-    msglen += 24+IMDHEADERSIZE;
-  }
-  if (imdsinfo->box) {
-    msglen += 9*4+IMDHEADERSIZE;
-  }
-  if (imdsinfo->coords) {
-    msglen += 3*4*num_coords+IMDHEADERSIZE;
-  }
-  if (imdsinfo->velocities) {
-    msglen += 3*4*num_coords+IMDHEADERSIZE;
-  }
-  if (imdsinfo->forces) {
-    msglen += 3*4*num_coords+IMDHEADERSIZE;
-  }
-  msgdata = new char[msglen];
-
   if (me == 0) {
     /* set up incoming socket on MPI rank 0. */
     imdsock_init();
@@ -638,6 +642,7 @@ FixIMD::FixIMD(LAMMPS *lmp, int narg, char **arg) :
  *********************************/
 FixIMD::~FixIMD()
 {
+
 #if defined(LAMMPS_ASYNC_IMD)
   if (me == 0) {
     pthread_mutex_lock(&write_mutex);
@@ -657,12 +662,12 @@ FixIMD::~FixIMD()
   memory->destroy(vel_data);
   memory->destroy(force_data);
 
-  memory->destroy(msgdata);
+  delete[] msgdata;
   memory->destroy(recv_force_buf);
   taginthash_destroy(hashtable);
   delete hashtable;
   free(rev_idmap);
-  free(imdsinfo);
+  delete imdsinfo;
   // close sockets
   imdsock_shutdown(clientsock);
   imdsock_destroy(clientsock);
@@ -763,6 +768,103 @@ int FixIMD::reconnect()
 /* wait for IMD client (e.g. VMD) to respond, initialize communication
  * buffers and collect tag/id maps. */
 void FixIMD::setup(int)
+{
+  if (imd_version == 2) {
+    setup_v2();
+  }
+  else {
+    setup_v3();
+  }
+}
+
+void FixIMD::setup_v2() {
+  /* nme:    number of atoms in group on this MPI task
+   * nmax:   max number of atoms in group across all MPI tasks
+   * nlocal: all local atoms
+   */
+  int i,j;
+  int nmax,nme,nlocal;
+  int *mask  = atom->mask;
+  tagint *tag  = atom->tag;
+  nlocal = atom->nlocal;
+  nme=0;
+  for (i=0; i < nlocal; ++i)
+    if (mask[i] & groupbit) ++nme;
+
+  MPI_Allreduce(&nme,&nmax,1,MPI_INT,MPI_MAX,world);
+  memory->destroy(coord_data);
+  maxbuf = nmax*size_one;
+  coord_data = (void *) memory->smalloc(maxbuf,"imd:coord_data");
+
+  connect_msg = 1;
+  reconnect();
+  MPI_Bcast(&imd_inactive, 1, MPI_INT, 0, world);
+  MPI_Bcast(&imd_terminate, 1, MPI_INT, 0, world);
+  if (imd_terminate)
+    error->all(FLERR,"LAMMPS terminated on error in setting up IMD connection.");
+
+  /* initialize and build hashtable. */
+  auto hashtable=new taginthash_t;
+  taginthash_init(hashtable, num_coords);
+  idmap = (void *)hashtable;
+
+  int tmp, ndata;
+  auto buf = static_cast<struct commdata *>(coord_data);
+
+  if (me == 0) {
+    MPI_Status status;
+    MPI_Request request;
+    auto taglist = new tagint[num_coords];
+    int numtag=0; /* counter to map atom tags to a 0-based consecutive index list */
+
+    for (i=0; i < nlocal; ++i) {
+      if (mask[i] & groupbit) {
+        taglist[numtag] = tag[i];
+        ++numtag;
+      }
+    }
+
+    /* loop over procs to receive remote data */
+    for (i=1; i < comm->nprocs; ++i) {
+      MPI_Irecv(coord_data, maxbuf, MPI_BYTE, i, 0, world, &request);
+      MPI_Send(&tmp, 0, MPI_INT, i, 0, world);
+      MPI_Wait(&request, &status);
+      MPI_Get_count(&status, MPI_BYTE, &ndata);
+      ndata /= size_one;
+
+      for (j=0; j < ndata; ++j) {
+        taglist[numtag] = buf[j].tag;
+        ++numtag;
+      }
+    }
+
+    /* sort list of tags by value to have consistently the
+     * same list when running in parallel and build hash table. */
+    id_sort(taglist, 0, num_coords-1);
+    for (i=0; i < num_coords; ++i) {
+      taginthash_insert(hashtable, taglist[i], i);
+    }
+    delete[] taglist;
+
+    /* generate reverse index-to-tag map for communicating
+     * IMD forces back to the proper atoms */
+    rev_idmap=taginthash_keys(hashtable);
+  } else {
+    nme=0;
+    for (i=0; i < nlocal; ++i) {
+      if (mask[i] & groupbit) {
+        buf[nme].tag = tag[i];
+        ++nme;
+      }
+    }
+    /* blocking receive to wait until it is our turn to send data. */
+    MPI_Recv(&tmp, 0, MPI_INT, 0, 0, world, MPI_STATUS_IGNORE);
+    MPI_Rsend(coord_data, nme*size_one, MPI_BYTE, 0, 0, world);
+  }
+
+  }
+
+void FixIMD::setup_v3() 
 {
   /* nme:    number of atoms in group on this MPI task
    * nmax:   max number of atoms in group across all MPI tasks
@@ -807,11 +909,24 @@ void FixIMD::setup(int)
   idmap = (void *)hashtable;
 
   int tmp, ndata;
-  auto buf = static_cast<struct commdata *>(coord_data);
+
+  struct commdata *buf = nullptr;
+  if (imdsinfo->coords) {
+    buf = static_cast<struct commdata *>(coord_data);
+  }
+  else if (imdsinfo->velocities) {
+    buf = static_cast<struct commdata *>(vel_data);
+  }
+  else if (imdsinfo->forces) {
+    buf = static_cast<struct commdata *>(force_data);
+  }
 
   if (me == 0) {
-    std::vector<MPI_Status> statuses;
-    std::vector<MPI_Request> requests;
+    if (buf == nullptr) {
+      return;
+    }
+    MPI_Status status;
+    MPI_Request request;
     auto taglist = new tagint[num_coords];
     int numtag=0; /* counter to map atom tags to a 0-based consecutive index list */
 
@@ -824,39 +939,15 @@ void FixIMD::setup(int)
 
     /* loop over procs to receive remote data */
     for (i=1; i < comm->nprocs; ++i) {
-      /* We're assuming tags are consistent across x,v,f */
-      bool tag_recvd = false;
-      statuses.clear();
-      requests.clear();
-
-      if (imdsinfo->coords) {
-        requests.push_back(MPI_Request());
-        MPI_Irecv(coord_data, maxbuf, MPI_BYTE, i, 0, world, &requests.back());
-      }
-      if (imdsinfo->velocities) {
-        requests.push_back(MPI_Request());
-        MPI_Irecv(vel_data, maxbuf, MPI_BYTE, i, 0, world, &requests.back());
-      }
-      if (imdsinfo->forces) {
-        requests.push_back(MPI_Request());
-        MPI_Irecv(vel_data, maxbuf, MPI_BYTE, i, 0, world, &requests.back());
-      }
-      statuses.resize(requests.size());
+      MPI_Irecv(coord_data, maxbuf, MPI_BYTE, i, 0, world, &request);
       MPI_Send(&tmp, 0, MPI_INT, i, 0, world);
-      MPI_Waitall(requests.size(), requests.data(), statuses.data());
+      MPI_Wait(&request, &status);
+      MPI_Get_count(&status, MPI_BYTE, &ndata);
+      ndata /= size_one;
 
-      for (size_t k=0; k < statuses.size(); ++k) {
-        if (!tag_recvd) {
-          MPI_Get_count(&statuses[k], MPI_BYTE, &ndata);
-          ndata /= size_one;
-          for (j=0; j < ndata; ++j) {
-            taglist[numtag] = buf[j].tag;
-            ++numtag;
-          }
-          tag_recvd = true;
-        } else {
-          break;
-        }
+      for (j=0; j < ndata; ++j) {
+        taglist[numtag] = buf[j].tag;
+        ++numtag;
       }
     }
 
@@ -881,19 +972,10 @@ void FixIMD::setup(int)
     }
     /* blocking receive to wait until it is our turn to send data. */
     MPI_Recv(&tmp, 0, MPI_INT, 0, 0, world, MPI_STATUS_IGNORE);
-    if (imdsinfo->coords) {
-      MPI_Rsend(coord_data, nme*size_one, MPI_BYTE, 0, 0, world);
-    }
-    if (imdsinfo->velocities) {
-      MPI_Rsend(vel_data, nme*size_one, MPI_BYTE, 0, 0, world);
-    }
-    if (imdsinfo->forces) {
-      MPI_Rsend(force_data, nme*size_one, MPI_BYTE, 0, 0, world);
-    }
+    MPI_Rsend(coord_data, nme*size_one, MPI_BYTE, 0, 0, world);
   }
 
   }
-
 /* worker threads for asynchronous i/o */
 #if defined(LAMMPS_ASYNC_IMD)
 /* c bindings wrapper */
diff --git a/src/MISC/fix_imd.h b/src/MISC/fix_imd.h
index 6b8778dbf0..03d242f32b 100644
--- a/src/MISC/fix_imd.h
+++ b/src/MISC/fix_imd.h
@@ -116,6 +116,8 @@ class FixIMD : public Fix {
   char *msgdata;
 
  private:
+  void setup_v2();
+  void setup_v3();
   void handle_step_v2();
   void handle_client_input_v3();
   void handle_output_v3();