diff --git a/Basis/Basis.ml b/Basis/Basis.ml
index 9a3302f..3f417b6 100644
--- a/Basis/Basis.ml
+++ b/Basis/Basis.ml
@@ -4,6 +4,8 @@ type t =
     contracted_shells : ContractedShell.t array ;
     atomic_shells     : AtomicShell.t array lazy_t;
     general_basis     : GeneralBasis.t ;
+    range_separation  : float option ;
+    f12               : F12factor.t option ;
   }
 
 module As = AtomicShell
@@ -14,7 +16,7 @@ module Ps = PrimitiveShell
 let general_basis t = t.general_basis
 
 (** Returns an array of the basis set per atom *)
-let of_nuclei_and_general_basis nucl bas =
+let of_nuclei_and_general_basis ?f12 ?range_separation nucl bas =
   let index_ = ref 0 in
   let contracted_shells = 
     Array.map (fun (e, center) ->
@@ -52,15 +54,18 @@ let of_nuclei_and_general_basis nucl bas =
     |> Array.of_list
   ) in
   { contracted_shells ; atomic_shells ; size = !index_;
-    general_basis = bas }
+    general_basis = bas ; f12 ; range_separation }
 
 
-let size x = x.size
+let size t = t.size
 
-let atomic_shells x = Lazy.force x.atomic_shells
+let atomic_shells t = Lazy.force t.atomic_shells
 
-let contracted_shells x = x.contracted_shells
+let contracted_shells t = t.contracted_shells
 
+let range_separation t = t.range_separation
+
+let f12 t = t.f12
 
 
 let to_string b =
@@ -87,24 +92,24 @@ let to_string b =
 
 
 
-let of_nuclei_and_basis_filename ~nuclei filename = 
+let of_nuclei_and_basis_filename ?f12 ?range_separation ~nuclei filename = 
   let general_basis = 
     GeneralBasis.read filename
   in
-  of_nuclei_and_general_basis nuclei general_basis
+  of_nuclei_and_general_basis ?f12 ?range_separation nuclei general_basis
 
-let of_nuclei_and_basis_string ~nuclei str = 
+let of_nuclei_and_basis_string ?f12 ?range_separation ~nuclei str = 
   let general_basis = 
     GeneralBasis.of_string str
   in
-  of_nuclei_and_general_basis nuclei general_basis
+  of_nuclei_and_general_basis ?f12 ?range_separation nuclei general_basis
 
 
-let of_nuclei_and_basis_filenames ~nuclei filenames = 
+let of_nuclei_and_basis_filenames ?f12 ?range_separation ~nuclei filenames = 
   let general_basis = 
     GeneralBasis.read_many filenames
   in
-  of_nuclei_and_general_basis nuclei general_basis
+  of_nuclei_and_general_basis ?f12 ?range_separation nuclei general_basis
 
 
 let pp ppf t =
diff --git a/Basis/Basis.mli b/Basis/Basis.mli
index ea9297e..f9cac65 100644
--- a/Basis/Basis.mli
+++ b/Basis/Basis.mli
@@ -3,7 +3,8 @@
 type t 
 
 
-val of_nuclei_and_general_basis : Nuclei.t -> GeneralBasis.t -> t
+val of_nuclei_and_general_basis : ?f12:F12factor.t -> ?range_separation:float ->
+                                  Nuclei.t -> GeneralBasis.t -> t
 (** Takes an array of {!Nuclei.t}, and a {!GeneralBasis.t} (such as cc-pVDZ
   for instance) and creates the corresponding atomic basis set.
   All the {!Element.t}'s of the array of {!Nuclei.t} are searched in 
@@ -13,17 +14,20 @@ val of_nuclei_and_general_basis : Nuclei.t -> GeneralBasis.t -> t
 *)
 
 
-val of_nuclei_and_basis_filename : nuclei:Nuclei.t -> string -> t
+val of_nuclei_and_basis_filename : ?f12:F12factor.t -> ?range_separation:float ->
+                                   nuclei:Nuclei.t -> string -> t
 (** Same as {!of_nuclei_and_general_basis}, but taking the {!GeneralBasis.t}
   from a file. 
   *)
 
-val of_nuclei_and_basis_string : nuclei:Nuclei.t -> string -> t
+val of_nuclei_and_basis_string : ?f12:F12factor.t -> ?range_separation:float ->
+                                 nuclei:Nuclei.t -> string -> t
 (** Same as {!of_nuclei_and_general_basis}, but taking the {!GeneralBasis.t}
   from a string. 
   *)
 
-val of_nuclei_and_basis_filenames : nuclei:Nuclei.t -> string list -> t
+val of_nuclei_and_basis_filenames : ?f12:F12factor.t -> ?range_separation:float ->
+                                    nuclei:Nuclei.t -> string list -> t
 (** Same as {!of_nuclei_and_general_basis}, but taking the {!GeneralBasis.t}
   from multiple files. 
   *)
@@ -41,6 +45,12 @@ val contracted_shells : t -> ContractedShell.t array
 val general_basis : t -> GeneralBasis.t
 (** Returns the [!GeneralBasis] that was used to build the current basis. *)
 
+val f12 : t -> F12factor.t option
+(** Returns the explicit correlation factor if present. *)
+
+val range_separation : t -> float option
+(** Returns the electron-electrons interaction range-separation value if present. *)
+
 (** {2 Printers} *)
 
 val to_string : t -> string