diff --git a/Parallel_mpi/Parallel.ml b/Parallel_mpi/Parallel.ml
index 5fff1dd..92353ba 100644
--- a/Parallel_mpi/Parallel.ml
+++ b/Parallel_mpi/Parallel.ml
@@ -123,25 +123,18 @@ module InterNode = struct
       Mpi.group_incl world_group ranks
     in
 
-    let result = 
-      Some (Mpi.comm_create Mpi.comm_world new_group)
-    in
-    try 
-      ignore @@ List.find (fun x -> x = world_rank) @@ Array.to_list ranks;
-      result
-    with Not_found -> None
+    Mpi.comm_create Mpi.comm_world new_group
 
 
   let rank = 
-    match comm with
-    | Some c-> Mpi.comm_rank c
-    | None -> -1
+    if comm <> Mpi.comm_none then
+      Mpi.comm_rank c
+    else 0
 
   let master = rank = 0
   
   let broadcast_generic broadcast x =
-    match comm with
-    | Some comm ->
+    if Mpi.comm_rank <> Mpi.comm_none then
       begin
         let x = 
           if master then Some (Lazy.force x)
@@ -150,15 +143,18 @@ module InterNode = struct
         match broadcast x 0 comm with
         | Some x -> x
         | None -> assert false
-      end
-    | None -> Lazy.force x
+    else
+      Lazy.force x
 
   let broadcast x = broadcast_generic Mpi.broadcast x
+(* TODO : temporary single-node fix
+  let broadcast x = Lazy.force x
+*)
 
   let barrier () =
-    match comm with
-    | Some comm -> Mpi.barrier comm 
-    | None -> ()
+    if comm <> Mpi.comm_none then
+      Mpi.barrier comm 
+    else ()
 
   let _ = barrier ()
 
diff --git a/Parallel_mpi/Parallel.mli b/Parallel_mpi/Parallel.mli
index 381656e..129ee50 100644
--- a/Parallel_mpi/Parallel.mli
+++ b/Parallel_mpi/Parallel.mli
@@ -60,7 +60,7 @@ end
 (** {5 Inter-node  operations} *)
 module InterNode : sig
 
-  val comm : Mpi.communicator option
+  val comm : Mpi.communicator 
   (** MPI Communicator among the master processes of the each node *)
 
   val rank : Mpi.rank
diff --git a/run_fci_f12.ml b/run_fci_f12.ml
index c1521a3..0653f6a 100644
--- a/run_fci_f12.ml
+++ b/run_fci_f12.ml
@@ -96,7 +96,7 @@ let () =
     Simulation.of_filenames ~f12 ~charge ~multiplicity ~nuclei:nuclei_file basis_file
   in
 
-  let hf = HartreeFock.make ~guess:`Huckel simulation in
+  let hf = HartreeFock.make ~guess:`Hcore simulation in
   if Parallel.master then
     Format.fprintf ppf "@[%a@]@." HartreeFock.pp hf;