let () =
  let open Command_line in
  begin
    set_header_doc (Sys.argv.(0) ^ " - QCaml command");
    set_description_doc "Runs a Hartree-Fock calculation";
    set_specs
      [ { short='b' ; long="basis" ; opt=Mandatory;
          arg=With_arg "<string>";
          doc="Name of the file containing the basis set"; } ;

        { short='x' ; long="xyz" ; opt=Mandatory;
          arg=With_arg "<string>";
          doc="Name of the file containing the nuclear coordinates in xyz format"; } ;

        { short='m' ; long="multiplicity" ; opt=Optional;
          arg=With_arg "<int>";
          doc="Spin multiplicity (2S+1). Default is singlet"; } ;

        { short='c' ; long="charge" ; opt=Optional;
          arg=With_arg "<int>";
          doc="Total charge of the molecule. Default is 0"; } ;
      ]
  end;

  (* Handle options *)
  let basis_file  = Util.of_some @@ Command_line.get "basis" in

  let nuclei_file = Util.of_some @@ Command_line.get "xyz" in

  let charge = 
    match Command_line.get "charge" with
    | Some x -> int_of_string x
    | None   -> 0
  in

  let multiplicity =
    match Command_line.get "multiplicity" with
    | Some x -> int_of_string x
    | None -> 1
  in

  let ppf = 
    if Parallel.master then Format.std_formatter
    else Printing.ppf_dev_null
  in

  let s =
    Simulation.of_filenames ~charge ~multiplicity ~nuclei:nuclei_file basis_file
  in

  let hf = HartreeFock.make s in
  Format.fprintf ppf "@[%a@]@." HartreeFock.pp hf;

  let mos =
    MOBasis.of_hartree_fock hf
  in

  let space =
    DeterminantSpace.fci_of_mo_basis  ~frozen_core:false  mos
  in
  let ci = CI.make space in
  Format.fprintf ppf "FCI energy : %20.16f@." ((CI.eigenvalues ci).{1} +. Simulation.nuclear_repulsion s);
  (*
  let s2 = Util.xt_o_x ~o:(CI.s2_matrix ci) ~x:(CI.eigenvectors ci) in
  Util.list_range 1 (DeterminantSpace.size space)
  |> List.iter (fun i -> Format.printf "@[%f@]@;" s2.{i,i});
  *)