diff --git a/configure b/configure
index 7dd91bf3..1c925432 100755
--- a/configure
+++ b/configure
@@ -204,6 +204,7 @@ EOF
               cd trexio-${VERSION}
               ./configure --prefix=\${QP_ROOT}
               make -j 8 && make -j 8 check && make -j 8 install
+              cp ${QP_ROOT}/include/trexio_f.f90 ${QP_ROOT}/src/ezfio_files
 EOF
 
     elif [[ ${PACKAGE} = gmp ]] ; then
diff --git a/scripts/compilation/qp_create_ninja b/scripts/compilation/qp_create_ninja
index c0ba8c6a..ad9a223b 100755
--- a/scripts/compilation/qp_create_ninja
+++ b/scripts/compilation/qp_create_ninja
@@ -40,7 +40,7 @@ from qp_path import QP_ROOT, QP_SRC, QP_EZFIO
 
 LIB = " -lz"
 EZFIO_LIB = join("$QP_ROOT", "lib", "libezfio_irp.a")
-ZMQ_LIB = join("$QP_ROOT", "lib", "libf77zmq.a") + " "  + join("$QP_ROOT", "lib", "libzmq.a") + " -lstdc++ -lrt -ldl"
+ZMQ_LIB = join("$QP_ROOT", "lib", "libf77zmq.a") + " "  + join("$QP_ROOT", "lib", "libzmq.a") + " -ltrexio -lstdc++ -lrt -ldl"
 ROOT_BUILD_NINJA = join("$QP_ROOT", "config", "build.ninja")
 ROOT_BUILD_NINJA_EXP =  join(QP_ROOT, "config", "build.ninja")
 ROOT_BUILD_NINJA_EXP_tmp =  join(QP_ROOT, "config", "build.ninja.tmp")
diff --git a/scripts/save_current_mos.sh b/scripts/save_current_mos.sh
deleted file mode 100755
index cf4c5471..00000000
--- a/scripts/save_current_mos.sh
+++ /dev/null
@@ -1,45 +0,0 @@
-#!/bin/bash
-# This script is used by the MOs module, and should not be used by users.
-# It copies the EZFIO/mo_basis directory in the save/EZFIO/mo_basis/xxx
-# directory, where xxx is the corresponding mo_label.
-# Wed Apr  2 14:35:15 CEST 2014
-
-
-if [[ -z ${QP_ROOT} ]] ; then
-  print "The QP_ROOT environment variable is not set."
-  print "Please reload the quantum_package.rc file."
-  exit -1
-fi
-
-EZFIO="$1"
-
-if [[ -z "${EZFIO}" ]] ; then
-  echo "Error in $0"
-  exit 1
-fi
-
-if [[ ! -f "${EZFIO}/mo_basis/mo_label" ]] ; then
-  LABEL='no_label'
-else
-  LABEL=$(head -1 "${EZFIO}/mo_basis/mo_label" | xargs) #xargs trims the result
-fi
-
-DESTINATION="save/mo_basis/${LABEL}"
-
-cd "${EZFIO}"
-
-if [[ ! -d save/mo_basis ]] ; then
-        mkdir -p save/mo_basis
-fi
-
-BACKUP="${DESTINATION}.old"
-if [[ -d "${BACKUP}" ]] ; then
-        rm -rf "${BACKUP}"
-fi
-
-if [[ -d "${DESTINATION}" ]] ; then
-        mv "${DESTINATION}" "${BACKUP}"
-fi
-
-cp -r mo_basis "${DESTINATION}"
-
diff --git a/src/dummy/NEED b/src/dummy/NEED
deleted file mode 100644
index 3d5eb1f7..00000000
--- a/src/dummy/NEED
+++ /dev/null
@@ -1,48 +0,0 @@
-ao_basis
-ao_one_e_ints
-ao_two_e_erf_ints
-ao_two_e_ints
-aux_quantities
-becke_numerical_grid
-bitmask
-cipsi
-cis
-cisd
-davidson
-davidson_dressed
-davidson_undressed
-density_for_dft
-determinants
-dft_keywords
-dft_utils_in_r
-dft_utils_func
-dressing
-electrons
-ezfio_files
-fci
-functionals
-generators_cas
-generators_full
-hartree_fock
-iterations
-kohn_sham
-kohn_sham_rs
-mo_basis
-mo_guess
-mo_one_e_ints
-mo_two_e_erf_ints
-mo_two_e_ints
-mpi
-nuclei
-perturbation
-pseudo
-psiref_cas
-psiref_utils
-scf_utils
-selectors_cassd
-selectors_full
-selectors_utils
-single_ref_method
-tools
-utils
-zmq
diff --git a/src/dummy/README.rst b/src/dummy/README.rst
deleted file mode 100644
index 6bdb2ca7..00000000
--- a/src/dummy/README.rst
+++ /dev/null
@@ -1,6 +0,0 @@
-=====
-dummy
-=====
-
-Module necessary to avoid the ``xxx  is a root module but does not contain a main file`` message.
-
diff --git a/src/dummy/dummy.main.irp.f b/src/dummy/dummy.main.irp.f
deleted file mode 100644
index 0b789ea1..00000000
--- a/src/dummy/dummy.main.irp.f
+++ /dev/null
@@ -1,7 +0,0 @@
-program dummy
-  implicit none
-  BEGIN_DOC
-! Dummy test file
-  END_DOC
-  print *,  'OK'
-end
diff --git a/src/mo_basis/mo_class.irp.f b/src/mo_basis/mo_class.irp.f
index 95fbb443..b6e993a4 100644
--- a/src/mo_basis/mo_class.irp.f
+++ b/src/mo_basis/mo_class.irp.f
@@ -1,7 +1,4 @@
-! DO NOT MODIFY BY HAND
-! Created by $QP_ROOT/scripts/ezfio_interface/ei_handler.py
-! from file /home/eginer/programs/qp2/src/mo_basis/EZFIO.cfg
-
+use trexio
 
 BEGIN_PROVIDER [ character*(32), mo_class , (mo_num) ]
   implicit none
@@ -10,16 +7,27 @@ BEGIN_PROVIDER [ character*(32), mo_class , (mo_num) ]
   END_DOC
 
   logical                        :: has
-  PROVIDE ezfio_filename
+  integer(trexio_exit_code)      :: rc
+
+  PROVIDE ezfio_filename trexio_file
+
+  mo_class(:) = 'Active'
+
   if (mpi_master) then
     if (size(mo_class) == 0) return
 
-    call ezfio_has_mo_basis_mo_class(has)
-    if (has) then
-      write(6,'(A)') '.. >>>>> [ IO READ: mo_class ] <<<<< ..'
-      call ezfio_get_mo_basis_mo_class(mo_class)
+    if (use_trexio) then
+      rc = trexio_has_mo_class(trexio_file)
+      if (rc == TREXIO_SUCCESS) then
+        rc = trexio_read_mo_class(trexio_file, mo_class, len(mo_class(1)))
+        call trexio_assert(rc, TREXIO_SUCCESS)
+      endif
     else
-      mo_class(:) = 'Active'
+      call ezfio_has_mo_basis_mo_class(has)
+      if (has) then
+        write(6,'(A)') '.. >>>>> [ IO READ: mo_class ] <<<<< ..'
+        call ezfio_get_mo_basis_mo_class(mo_class)
+      endif
     endif
   endif
   IRP_IF MPI_DEBUG
diff --git a/src/mo_basis/mos.irp.f b/src/mo_basis/mos.irp.f
index 57ebb533..9211abc9 100644
--- a/src/mo_basis/mos.irp.f
+++ b/src/mo_basis/mos.irp.f
@@ -1,3 +1,4 @@
+use trexio
 BEGIN_PROVIDER [ integer, mo_num ]
   implicit none
   BEGIN_DOC
@@ -5,37 +6,51 @@ BEGIN_PROVIDER [ integer, mo_num ]
   END_DOC
 
   logical                        :: has
-  PROVIDE ezfio_filename
+  integer                        :: ierr
+  integer(trexio_exit_code)      :: rc
+
+  PROVIDE ezfio_filename trexio_file
+
   if (mpi_master) then
-    call ezfio_has_mo_basis_mo_num(has)
-  endif
-  IRP_IF MPI_DEBUG
-    print *,  irp_here, mpi_rank
-    call MPI_BARRIER(MPI_COMM_WORLD, ierr)
-  IRP_ENDIF
-  IRP_IF MPI
-    include 'mpif.h'
-    integer                        :: ierr
-    call MPI_BCAST( has, 1, MPI_LOGICAL, 0, MPI_COMM_WORLD, ierr)
-    if (ierr /= MPI_SUCCESS) then
-      stop 'Unable to read mo_num with MPI'
-    endif
-  IRP_ENDIF
-  if (.not.has) then
-    mo_num = ao_ortho_canonical_num
-  else
-    if (mpi_master) then
-      call ezfio_get_mo_basis_mo_num(mo_num)
+    if (use_trexio) then
+      rc = trexio_has_mo_num(trexio_file)
+      has = (rc == TREXIO_SUCCESS)
+    else
+      call ezfio_has_mo_basis_mo_num(has)
     endif
+    IRP_IF MPI_DEBUG
+      print *,  irp_here, mpi_rank
+      call MPI_BARRIER(MPI_COMM_WORLD, ierr)
+    IRP_ENDIF
     IRP_IF MPI
-      call MPI_BCAST( mo_num, 1, MPI_INTEGER, 0, MPI_COMM_WORLD, ierr)
+      include 'mpif.h'
+      call MPI_BCAST( has, 1, MPI_LOGICAL, 0, MPI_COMM_WORLD, ierr)
       if (ierr /= MPI_SUCCESS) then
         stop 'Unable to read mo_num with MPI'
       endif
     IRP_ENDIF
+    if (.not.has) then
+      mo_num = ao_ortho_canonical_num
+    else
+      if (mpi_master) then
+        if (use_trexio) then
+          rc = trexio_read_mo_num(trexio_file, mo_num)
+          call trexio_assert(rc, TREXIO_SUCCESS)
+        else
+          call ezfio_get_mo_basis_mo_num(mo_num)
+        endif
+      endif
+
+      IRP_IF MPI
+        call MPI_BCAST( mo_num, 1, MPI_INTEGER, 0, MPI_COMM_WORLD, ierr)
+        if (ierr /= MPI_SUCCESS) then
+          stop 'Unable to read mo_num with MPI'
+        endif
+      IRP_ENDIF
+    endif
+    call write_int(6,mo_num,'mo_num')
+    ASSERT (mo_num > 0)
   endif
-  call write_int(6,mo_num,'mo_num')
-  ASSERT (mo_num > 0)
 
 END_PROVIDER
 
@@ -52,12 +67,16 @@ BEGIN_PROVIDER [ double precision, mo_coef, (ao_num,mo_num) ]
   integer                        :: i, j
   double precision, allocatable  :: buffer(:,:)
   logical                        :: exists
-  PROVIDE ezfio_filename
-
+  integer(trexio_exit_code)      :: rc
+  PROVIDE ezfio_filename trexio_file
 
   if (mpi_master) then
-    ! Coefs
-    call ezfio_has_mo_basis_mo_coef(exists)
+    if (use_trexio) then
+      rc = trexio_has_mo_coefficient(trexio_file)
+      exists = (rc == TREXIO_SUCCESS)
+    else
+      call ezfio_has_mo_basis_mo_coef(exists)
+    endif
   endif
   IRP_IF MPI_DEBUG
     print *,  irp_here, mpi_rank
@@ -74,7 +93,12 @@ BEGIN_PROVIDER [ double precision, mo_coef, (ao_num,mo_num) ]
 
   if (exists) then
     if (mpi_master) then
-      call ezfio_get_mo_basis_mo_coef(mo_coef)
+      if (use_trexio) then
+          rc = trexio_read_mo_coefficient(trexio_file, mo_coef)
+          call trexio_assert(rc, TREXIO_SUCCESS)
+      else
+        call ezfio_get_mo_basis_mo_coef(mo_coef)
+      endif
       write(*,*) 'Read  mo_coef'
     endif
     IRP_IF MPI
@@ -105,12 +129,16 @@ BEGIN_PROVIDER [ double precision, mo_coef_imag, (ao_num,mo_num) ]
   integer                        :: i, j
   double precision, allocatable  :: buffer(:,:)
   logical                        :: exists
+  integer(trexio_exit_code)      :: rc
   PROVIDE ezfio_filename
 
-
   if (mpi_master) then
-    ! Coefs
-    call ezfio_has_mo_basis_mo_coef_imag(exists)
+    if (use_trexio) then
+      rc = trexio_has_mo_coefficient_im(trexio_file)
+      exists = (rc == TREXIO_SUCCESS)
+    else
+      call ezfio_has_mo_basis_mo_coef_imag(exists)
+    endif
   endif
   IRP_IF MPI_DEBUG
     print *,  irp_here, mpi_rank
@@ -127,7 +155,12 @@ BEGIN_PROVIDER [ double precision, mo_coef_imag, (ao_num,mo_num) ]
 
   if (exists) then
     if (mpi_master) then
-      call ezfio_get_mo_basis_mo_coef_imag(mo_coef_imag)
+      if (use_trexio) then
+          rc = trexio_read_mo_coefficient_im(trexio_file, mo_coef_imag)
+          call trexio_assert(rc, TREXIO_SUCCESS)
+      else
+        call ezfio_get_mo_basis_mo_coef_imag(mo_coef_imag)
+      endif
       write(*,*) 'Read  mo_coef_imag'
     endif
     IRP_IF MPI
@@ -171,14 +204,27 @@ BEGIN_PROVIDER [ character*(64), mo_label ]
   END_DOC
 
   logical                        :: exists
+  integer(trexio_exit_code)      :: rc
+
   PROVIDE ezfio_filename
   if (mpi_master) then
-    call ezfio_has_mo_basis_mo_label(exists)
-    if (exists) then
-      call ezfio_get_mo_basis_mo_label(mo_label)
-      mo_label = trim(mo_label)
+    if (use_trexio) then
+      rc = trexio_has_mo_type(trexio_file)
+      if (rc == TREXIO_SUCCESS) then
+        rc = trexio_read_mo_type(trexio_file, mo_label, 64)
+        call trexio_assert(rc, TREXIO_SUCCESS)
+        mo_label = trim(mo_label)
+      else
+        mo_label = 'no_label'
+      endif
     else
-      mo_label = 'no_label'
+      call ezfio_has_mo_basis_mo_label(exists)
+      if (exists) then
+        call ezfio_get_mo_basis_mo_label(mo_label)
+        mo_label = trim(mo_label)
+      else
+        mo_label = 'no_label'
+      endif
     endif
     write(*,*) '* mo_label          ', trim(mo_label)
   endif
@@ -218,23 +264,34 @@ BEGIN_PROVIDER [ double precision, mo_occ, (mo_num) ]
   BEGIN_DOC
   ! |MO| occupation numbers
   END_DOC
+  integer(trexio_exit_code)      :: rc
   PROVIDE ezfio_filename elec_beta_num elec_alpha_num
+
+  mo_occ = 0.d0
+  integer :: i
+  do i=1,elec_beta_num
+    mo_occ(i) = 2.d0
+  enddo
+  do i=elec_beta_num+1,elec_alpha_num
+    mo_occ(i) = 1.d0
+  enddo
+
   if (mpi_master) then
-    logical :: exists
-    call ezfio_has_mo_basis_mo_occ(exists)
-    if (exists) then
-      call ezfio_get_mo_basis_mo_occ(mo_occ)
+    if (use_trexio) then
+      rc = trexio_has_mo_occupation(trexio_file)
+      if (rc == TREXIO_SUCCESS) then
+        rc = trexio_read_mo_occupation(trexio_file, mo_occ)
+        call trexio_assert(rc, TREXIO_SUCCESS)
+        write(*,*) 'Read mo_occ'
+      endif
     else
-      mo_occ = 0.d0
-      integer :: i
-      do i=1,elec_beta_num
-        mo_occ(i) = 2.d0
-      enddo
-      do i=elec_beta_num+1,elec_alpha_num
-        mo_occ(i) = 1.d0
-      enddo
+      logical :: exists
+      call ezfio_has_mo_basis_mo_occ(exists)
+      if (exists) then
+        call ezfio_get_mo_basis_mo_occ(mo_occ)
+        write(*,*) 'Read mo_occ'
+      endif
     endif
-    write(*,*) 'Read mo_occ'
   endif
   IRP_IF MPI_DEBUG
     print *,  irp_here, mpi_rank
diff --git a/src/mo_basis/utils.irp.f b/src/mo_basis/utils.irp.f
index 12c6c79d..23c47e95 100644
--- a/src/mo_basis/utils.irp.f
+++ b/src/mo_basis/utils.irp.f
@@ -1,58 +1,21 @@
 subroutine save_mos
   implicit none
-  double precision, allocatable  :: buffer(:,:)
-  integer                        :: i,j
-
-  call system('$QP_ROOT/scripts/save_current_mos.sh '//trim(ezfio_filename))
-  call ezfio_set_mo_basis_mo_num(mo_num)
-  call ezfio_set_mo_basis_mo_label(mo_label)
-  call ezfio_set_mo_basis_ao_md5(ao_md5)
-  allocate ( buffer(ao_num,mo_num) )
-  buffer = 0.d0
-  do j = 1, mo_num
-    do i = 1, ao_num
-      buffer(i,j) = mo_coef(i,j)
-    enddo
-  enddo
-  call ezfio_set_mo_basis_mo_coef(buffer)
-  call ezfio_set_mo_basis_mo_occ(mo_occ)
-  call ezfio_set_mo_basis_mo_class(mo_class)
-  deallocate (buffer)
-
-end
-
-
-subroutine save_mos_no_occ
-  implicit none
-  double precision, allocatable  :: buffer(:,:)
-  integer                        :: i,j
-
-  call system('$QP_ROOT/scripts/save_current_mos.sh '//trim(ezfio_filename))
- !call ezfio_set_mo_basis_mo_num(mo_num)
- !call ezfio_set_mo_basis_mo_label(mo_label)
- !call ezfio_set_mo_basis_ao_md5(ao_md5)
-  allocate ( buffer(ao_num,mo_num) )
-  buffer = 0.d0
-  do j = 1, mo_num
-    do i = 1, ao_num
-      buffer(i,j) = mo_coef(i,j)
-    enddo
-  enddo
-  call ezfio_set_mo_basis_mo_coef(buffer)
-  deallocate (buffer)
-
+  BEGIN_DOC
+! Write MO data to disk
+  END_DOC
+  call save_mos_truncated(mo_num)
 end
 
 subroutine save_mos_truncated(n)
+  use trexio
   implicit none
+  BEGIN_DOC
+! Saves the first n MOs
+  END_DOC
+  integer, intent(in)            :: n
   double precision, allocatable  :: buffer(:,:)
-  integer                        :: i,j,n
+  integer                        :: i,j
 
-  call system('$QP_ROOT/scripts/save_current_mos.sh '//trim(ezfio_filename))
-
-  call ezfio_set_mo_basis_mo_num(n)
-  call ezfio_set_mo_basis_mo_label(mo_label)
-  call ezfio_set_mo_basis_ao_md5(ao_md5)
   allocate ( buffer(ao_num,n) )
   buffer = 0.d0
   do j = 1, n
@@ -60,13 +23,97 @@ subroutine save_mos_truncated(n)
       buffer(i,j) = mo_coef(i,j)
     enddo
   enddo
-  call ezfio_set_mo_basis_mo_coef(buffer)
-  call ezfio_set_mo_basis_mo_occ(mo_occ)
-  call ezfio_set_mo_basis_mo_class(mo_class)
+  if (use_trexio) then
+    integer (trexio_exit_code) :: rc
+
+    rc = trexio_has_ao_num(trexio_file)
+    if (rc == TREXIO_HAS_NOT) then
+      rc = trexio_write_ao_num(trexio_file, ao_num)
+      call trexio_assert(rc, TREXIO_SUCCESS)
+    endif
+
+    rc = trexio_write_mo_num(trexio_file, n)
+    call trexio_assert(rc, TREXIO_SUCCESS)
+
+    rc = trexio_write_mo_type(trexio_file, mo_label, len(trim(mo_label)))
+    call trexio_assert(rc, TREXIO_SUCCESS)
+
+    rc = trexio_write_mo_occupation(trexio_file, mo_occ)
+    call trexio_assert(rc, TREXIO_SUCCESS)
+
+    rc = trexio_write_mo_class(trexio_file, mo_class, len(mo_class(1)))
+    call trexio_assert(rc, TREXIO_SUCCESS)
+
+    rc = trexio_write_mo_coefficient(trexio_file, buffer)
+    call trexio_assert(rc, TREXIO_SUCCESS)
+
+    rc = trexio_close(trexio_file)
+    call trexio_assert(rc, TREXIO_SUCCESS)
+    FREE trexio_file
+  else
+    call ezfio_set_mo_basis_mo_num(n)
+    call ezfio_set_mo_basis_mo_label(mo_label(1:n))
+    call ezfio_set_mo_basis_mo_occ(mo_occ(1:n))
+    call ezfio_set_mo_basis_mo_class(mo_class(1:n))
+    call ezfio_set_mo_basis_mo_coef(buffer)
+  endif
+  call ezfio_set_mo_basis_ao_md5(ao_md5)
+
   deallocate (buffer)
 
 end
 
+
+subroutine save_mo_coef
+  use trexio
+  implicit none
+  BEGIN_DOC
+! Saves the MO coefficients
+  END_DOC
+  double precision, allocatable  :: buffer(:,:)
+  integer                        :: i,j
+
+  allocate ( buffer(ao_num,mo_num) )
+  buffer = 0.d0
+  do j = 1, mo_num
+    do i = 1, ao_num
+      buffer(i,j) = mo_coef(i,j)
+    enddo
+  enddo
+  if (use_trexio) then
+    integer (trexio_exit_code) :: rc
+
+    rc = trexio_has_ao_num(trexio_file)
+    if (rc == TREXIO_HAS_NOT) then
+      rc = trexio_write_ao_num(trexio_file, ao_num)
+      call trexio_assert(rc, TREXIO_SUCCESS)
+    endif
+
+    rc = trexio_has_mo_num(trexio_file)
+    if (rc == TREXIO_HAS_NOT) then
+      rc = trexio_write_mo_num(trexio_file, mo_num)
+      call trexio_assert(rc, TREXIO_SUCCESS)
+    endif
+
+    rc = trexio_write_mo_coefficient(trexio_file, buffer)
+    call trexio_assert(rc, TREXIO_SUCCESS)
+
+    rc = trexio_close(trexio_file)
+    call trexio_assert(rc, TREXIO_SUCCESS)
+    FREE trexio_file
+  else
+    call ezfio_set_mo_basis_mo_coef(buffer)
+  endif
+  deallocate (buffer)
+
+end
+
+
+subroutine save_mos_no_occ
+  call save_mo_coef
+end
+
+
 subroutine mo_as_eigvectors_of_mo_matrix(matrix,n,m,label,sign,output)
   implicit none
   integer,intent(in)             :: n,m, sign
diff --git a/src/utils/EZFIO.cfg b/src/utils/EZFIO.cfg
index 7d367f0c..9e9a62f1 100644
--- a/src/utils/EZFIO.cfg
+++ b/src/utils/EZFIO.cfg
@@ -3,3 +3,4 @@ type: logical
 doc: If true, try to find symmetry in the MO coefficient matrices
 interface: ezfio,provider,ocaml
 default: False
+