diff --git a/.gitignore b/.gitignore
index 1a33ea8..81626aa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@
 _build
 .merlin
 *.install
+qcaml.opam
diff --git a/ao_basis/test/ao_basis_gaussian.ml b/ao_basis/test/ao_basis_gaussian.ml
new file mode 100644
index 0000000..9fa0b9f
--- /dev/null
+++ b/ao_basis/test/ao_basis_gaussian.ml
@@ -0,0 +1,125 @@
+open Alcotest
+open Qcaml_common
+open Qcaml_gaussian_integrals
+open Qcaml_gaussian_basis
+open Qcaml_ao_basis
+open Qcaml_particles
+open Qcaml_operators
+open Qcaml_linear_algebra
+open Ao_basis_gaussian
+
+let wd = Qcaml.root ^ Filename.dir_sep ^ "test"
+ 
+let make_tests name t =
+
+  let check_matrix title a r =
+    let ax =
+      Matrix.as_vec_inplace a
+      |> Vector.to_bigarray_inplace
+    in
+    Matrix.as_vec_inplace r
+    |> Vector.iteri (fun i x ->
+          let message =
+            Printf.sprintf "%s line %d" title i
+          in
+          check (float 1.e-10) message ax.{i} x
+        ) 
+  in
+
+  let check_eri a r =
+    let f { Eri.i_r1 ; j_r2 ; k_r1 ; l_r2 ; value } =
+      (i_r1, (j_r2, (k_r1, (l_r2, value))))
+    in
+    let a = Eri.to_list a |> List.rev_map f in
+    let r = Eri.to_list r |> List.rev_map f in
+    check (list (pair int (pair int (pair int (pair int (float 1.e-10)))))) "ERI" a r
+  in
+
+  let check_eri_lr a r =
+    let f { Eri_long_range.i_r1 ; j_r2 ; k_r1 ; l_r2 ; value } =
+      (i_r1, (j_r2, (k_r1, (l_r2, value))))
+    in
+    let a = Eri_long_range.to_list a |> List.rev_map f in
+    let r = Eri_long_range.to_list r |> List.rev_map f in
+    check (list (pair int (pair int (pair int (pair int (float 1.e-10)))))) "ERI_lr" a r
+  in
+
+  let test_overlap () =
+    let reference =
+      Matrix.sym_matrix_of_file (wd ^ Filename.dir_sep ^ name ^ "_overlap.ref")
+    in
+    let overlap =
+      Lazy.force t.overlap |> Overlap.matrix
+    in
+    check_matrix "Overlap" overlap reference
+  in
+
+  let test_eN_ints () =
+    let reference =
+      Matrix.sym_matrix_of_file (wd ^ Filename.dir_sep ^ name ^ "_nuc.ref")
+    in
+    let eN_ints =
+      Lazy.force t.eN_ints |> Electron_nucleus.matrix
+    in
+    check_matrix "eN_ints" eN_ints reference
+  in
+
+  let test_kin_ints () =
+    let reference =
+      Matrix.sym_matrix_of_file (wd ^ Filename.dir_sep ^ name ^  "_kin.ref")
+    in
+    let kin_ints =
+      Lazy.force t.kin_ints |> Kinetic.matrix
+    in
+    check_matrix "kin_ints" kin_ints reference
+  in
+
+  let test_ee_ints () =
+    let reference =
+      Eri.of_file (wd ^ Filename.dir_sep ^ name ^ "_eri.ref") ~sparsity:`Dense ~size:(Basis.size t.basis)
+    in
+    let ee_ints =
+      Lazy.force t.ee_ints
+    in
+    check_eri ee_ints reference
+    ;
+  in
+
+  let test_ee_lr_ints () =
+    let reference =
+      Eri_long_range.of_file (wd ^ Filename.dir_sep ^ name ^ "_eri_lr.ref") ~sparsity:`Dense
+          ~size:(Basis.size t.basis)
+    in
+    let ee_lr_ints =
+      Lazy.force t.ee_lr_ints
+    in
+    check_eri_lr ee_lr_ints reference
+  in
+
+  [
+    "Overlap",     `Quick,  test_overlap;
+    "eN_ints",     `Quick,  test_eN_ints;
+    "kin_ints",    `Quick,  test_kin_ints;
+    "ee_ints",     `Quick,  test_ee_ints;
+    "ee_lr_ints",  `Quick,  test_ee_lr_ints;
+  ]
+  
+let tests =
+  List.concat [ 
+    let nuclei =
+      wd ^ Filename.dir_sep ^ "water.xyz"
+    |> Nuclei.of_xyz_file 
+    in
+    let basis =
+      wd ^ Filename.dir_sep ^ "cc-pvdz"
+      |> Basis.of_nuclei_and_basis_filename ~nuclei
+    in
+    let rs = 0.5 in
+    let operators = [ Operator.of_range_separation rs ] in
+    let ao_basis = 
+      Ao_basis_gaussian.make ~basis ~operators nuclei
+    in
+    make_tests "water" ao_basis ;
+
+  ]
+    
diff --git a/ao_basis/test/dune b/ao_basis/test/dune
new file mode 100644
index 0000000..1af4abe
--- /dev/null
+++ b/ao_basis/test/dune
@@ -0,0 +1,10 @@
+(library
+ (name test_ao_basis)
+ (libraries
+  alcotest
+  qcaml.common
+  qcaml.linear_algebra
+  qcaml.gaussian_integrals
+  qcaml.ao_basis
+ )
+ (synopsis "Tests for the AO basis"))
diff --git a/linear_algebra/lib/conventions.ml b/linear_algebra/lib/conventions.ml
new file mode 100644
index 0000000..234394d
--- /dev/null
+++ b/linear_algebra/lib/conventions.ml
@@ -0,0 +1,28 @@
+(** Contains the conventions relative to the program.
+
+  The phase convention is given by:
+  {% $\sum_i c_i > 0$ %} or {% $\min_i c_i \ge  0$ %}
+
+*)
+
+let in_phase vec =
+  let s = Vector.sum vec in
+  if s = 0. then 
+    let rec first_non_zero k =
+      if k > Vector.dim vec then
+        k-1
+      else if Vector.at vec k = 0. then
+        first_non_zero (k+1)
+      else k
+    in
+    let k = first_non_zero 1 in
+    Vector.at vec k >= 0.
+  else
+    s > 0.
+
+
+let rephase mat  =
+  Matrix.to_col_vecs mat
+  |> Array.map (fun v -> if in_phase v then v else Vector.neg v)
+  |> Matrix.of_col_vecs
+
diff --git a/linear_algebra/lib/conventions.mli b/linear_algebra/lib/conventions.mli
new file mode 100644
index 0000000..60da2d3
--- /dev/null
+++ b/linear_algebra/lib/conventions.mli
@@ -0,0 +1,14 @@
+(** Contains the conventions relative to the program.
+
+  The phase convention is given by:
+  {% $\sum_i c_i > 0$ %} or {% $\min_i c_i \ge  0$ %}
+
+*)
+
+
+val in_phase : 'a Vector.t -> bool
+(** Checks if one MO respects the phase convention *)
+
+val rephase : ('a,'b) Matrix.t -> ('a,'b) Matrix.t
+(** Apply the phase convention to the MOs. *)
+