diff --git a/config/gfortran.cfg b/config/gfortran.cfg
index 342acae9..ec72e722 100644
--- a/config/gfortran.cfg
+++ b/config/gfortran.cfg
@@ -13,7 +13,7 @@
 FC           : gfortran -g -ffree-line-length-none -I . -fPIC
 LAPACK_LIB   : -lblas -llapack
 IRPF90       : irpf90
-IRPF90_FLAGS : --ninja --align=32 --assert 
+IRPF90_FLAGS : --ninja --align=32 --assert -DGNU_CHECK_OMP
 
 # Global options
 ################
diff --git a/config/ifort.cfg b/config/ifort.cfg
index 714c4b10..0382360a 100644
--- a/config/ifort.cfg
+++ b/config/ifort.cfg
@@ -9,7 +9,7 @@
 FC           : ifort -fpic
 LAPACK_LIB   : -mkl=parallel -lirc -lsvml -limf -lipps
 IRPF90       : irpf90
-IRPF90_FLAGS : --ninja --align=32  -DINTEL
+IRPF90_FLAGS : --ninja --align=32 -DINTEL
 
 # Global options
 ################
diff --git a/config/ifort_debug.cfg b/config/ifort_debug.cfg
index 9b718380..d70b1465 100644
--- a/config/ifort_debug.cfg
+++ b/config/ifort_debug.cfg
@@ -9,7 +9,7 @@
 FC           : ifort -fpic
 LAPACK_LIB   : -mkl=parallel -lirc -lsvml -limf -lipps
 IRPF90       : irpf90
-IRPF90_FLAGS : --ninja --align=32  --assert -DINTEL
+IRPF90_FLAGS : --ninja --align=32 --assert -DINTEL
 
 # Global options
 ################
diff --git a/config/ifort_rome.cfg b/config/ifort_rome.cfg
index 5ed01227..1ac78717 100644
--- a/config/ifort_rome.cfg
+++ b/config/ifort_rome.cfg
@@ -9,7 +9,7 @@
 FC           : ifort -fpic
 LAPACK_LIB   : -mkl=parallel -lirc -lsvml -limf -lipps
 IRPF90       : irpf90
-IRPF90_FLAGS : --ninja --align=32  -DINTEL
+IRPF90_FLAGS : --ninja --align=32 -DINTEL
 
 # Global options
 ################
diff --git a/scripts/verif_omp/check_actual_setup.sh b/scripts/verif_omp/check_actual_setup.sh
new file mode 100755
index 00000000..6eaa4517
--- /dev/null
+++ b/scripts/verif_omp/check_actual_setup.sh
@@ -0,0 +1,12 @@
+#!/bin/sh
+
+# go in qp2/src/fci to run check_omp_actual_setup
+# to see if we can run in parallel an omp section in another one
+echo ""
+echo "Please wait..."
+echo ""
+cd ../../src/fci
+ninja || echo "Please recompile from the root"  
+echo ""
+./check_omp_actual_setup
+cd ../../scripts/verif_omp
diff --git a/scripts/verif_omp/check_omp_v2.f90 b/scripts/verif_omp/check_omp_v2.f90
new file mode 100644
index 00000000..ca6af8bd
--- /dev/null
+++ b/scripts/verif_omp/check_omp_v2.f90
@@ -0,0 +1,175 @@
+program check_omp_v2
+ 
+  use omp_lib
+
+  implicit none
+
+  integer :: accu, accu2
+  integer :: s, n_setting
+  logical :: verbose, test_versions
+  logical, allocatable :: is_working(:)
+
+  verbose = .False.
+  test_versions = .True.
+  n_setting = 4
+
+  allocate(is_working(n_setting))
+
+  is_working = .False.
+
+  ! set the number of threads
+  call omp_set_num_threads(2) 
+
+  do s = 1, n_setting
+
+    accu = 0
+    accu2 = 0
+
+    call omp_set_max_active_levels(1)
+    call omp_set_nested(.False.)
+
+    if (s==1) then
+      !call set_multiple_levels_omp()
+      cycle
+    elseif (s==2) then
+      call omp_set_max_active_levels(5)
+    elseif (s==3) then
+      call omp_set_nested(.True.)
+    else
+      call omp_set_nested(.True.)
+      call omp_set_max_active_levels(5)
+    endif
+
+    ! Level 1
+    !$OMP PARALLEL 
+      if (verbose) then
+        print*,'Num threads level 1:',omp_get_num_threads()
+      endif
+
+      ! Level 2
+      !$OMP PARALLEL 
+        if (verbose) then
+          print*,'Num threads level 2:',omp_get_num_threads()
+        endif
+
+        ! Level 3
+        !$OMP PARALLEL 
+          if (verbose) then
+            print*,'Num threads level 3:',omp_get_num_threads()
+          endif
+
+          call check_omp_in_subroutine(accu2)
+     
+          ! Level 4
+          !$OMP PARALLEL 
+
+            if (verbose) then
+              print*,'Num threads level 4:',omp_get_num_threads()
+            endif
+
+           !$OMP ATOMIC    
+           accu = accu + 1
+           !$OMP END ATOMIC 
+       
+          !$OMP END PARALLEL
+     
+     
+        !$OMP END PARALLEL
+
+
+      !$OMP END PARALLEL
+
+
+    !$OMP END PARALLEL
+
+  if (verbose) then
+    print*,'Setting:',s,'accu=',accu
+    print*,'Setting:',s,'accu2=',accu2
+  endif
+
+  if (accu == 16 .and. accu2 == 16) then
+    is_working(s) = .True.
+  endif
+
+  enddo
+
+  if (verbose) then
+    if (is_working(2)) then
+      print*,'The parallelization works on 4 levels with:'
+      print*,'call omp_set_max_active_levels(5)'
+      print*,''
+      print*,'Please use the irpf90 flags -DSET_MAX_ACT in qp2/config/${compiler_name}.cfg'
+    elseif (is_working(3)) then
+      print*,'The parallelization works on 4 levels with:'
+      print*,'call omp_set_nested(.True.)'
+      print*,''
+      print*,'Please use the irpf90 flag -DSET_NESTED in qp2/config/${compiler_name}.cfg'
+    elseif (is_working(4)) then
+      print*,'The parallelization works on 4 levels with:'
+      print*,'call omp_set_nested(.True.)'
+      print*,'+'
+      print*,'call omp_set_max_active_levels(5)'
+      print*,''
+      print*,'Please use the irpf90 flags -DSET_NESTED -DSET_MAX_ACT in qp2/config/${compiler_name}.cfg'
+    else
+      print*,'The parallelization on multiple levels does not work with:'
+      print*,'call omp_set_max_active_levels(5)'
+      print*,'or'
+      print*,'call omp_set_nested(.True.)'
+      print*,'or'
+      print*,'call omp_set_nested(.True.)'
+      print*,'+'
+      print*,'call omp_set_max_active_levels(5)'
+      print*,''
+      print*,'Try an other compiler and good luck...'
+    endif
+
+   ! if (is_working(1)) then
+   !   print*,''
+   !   print*,'=========================================================='
+   !   print*,'Your actual set up works for parallelization with 4 levels'
+   !   print*,'=========================================================='
+   !   print*,''
+   ! else
+   !   print*,''
+   !   print*,'==================================================================='
+   !   print*,'Your actual set up does not work for parallelization with 4 levels'
+   !   print*,'Please look at the previous messages to understand the requirements'
+   !   print*,'==================================================================='
+   !   print*,''
+   ! endif
+  endif
+
+  ! List of working flags
+  if (test_versions) then
+    print*,'Tests:',is_working(2:4)
+  endif
+
+  ! IRPF90_FLAGS
+  if (is_working(2)) then
+    print*,'-DSET_MAX_ACT'
+  elseif (is_working(3)) then
+    print*,'-DSET_NESTED'
+  elseif (is_working(4)) then
+    print*,'-DSET_MAX_ACT -DSET_NESTED'
+  else
+    print*,'ERROR'
+  endif
+
+end
+
+subroutine check_omp_in_subroutine(accu2)
+
+  implicit none
+ 
+  integer, intent(inout) :: accu2
+
+  !$OMP PARALLEL
+
+  !$OMP ATOMIC
+  accu2 = accu2 + 1
+  !$OMP END ATOMIC
+
+  !$OMP END PARALLEL
+
+end
diff --git a/scripts/verif_omp/check_required_setup.sh b/scripts/verif_omp/check_required_setup.sh
new file mode 100755
index 00000000..facb6cbb
--- /dev/null
+++ b/scripts/verif_omp/check_required_setup.sh
@@ -0,0 +1,19 @@
+#!/bin/sh
+
+# take one argument which is the compiler used
+# return the required IRPF90_FLAGS for the $1 compiler
+
+if [ -z "$1" ]
+then
+    echo "Give the compiler in argument"
+else
+
+$1 --version > /dev/null \
+&& $1 -O0 -fopenmp check_omp_v2.f90 \
+&& ./a.out | tail -n 1
+
+
+# if there is an error or if the compiler is not found
+$1 --version > /dev/null || echo 'compiler not found'
+
+fi
diff --git a/scripts/verif_omp/study_omp.sh b/scripts/verif_omp/study_omp.sh
new file mode 100755
index 00000000..00668d59
--- /dev/null
+++ b/scripts/verif_omp/study_omp.sh
@@ -0,0 +1,30 @@
+#!/bin/sh
+
+# list of compilers
+list_comp="ifort gfortran-7 gfortran-8 gfortran-9"
+
+# file to store the results
+FILE=results.dat
+
+touch $FILE
+rm $FILE
+
+# Comments
+echo "1: omp_set_max_active_levels(5)" >> $FILE
+echo "2: omp_set_nested(.True.)" >> $FILE
+echo "3: 1 + 2" >> $FILE
+echo "" >> $FILE
+echo "1 2 3" >> $FILE
+
+# loop on the comp
+for comp in $list_comp
+do
+	$comp --version > /dev/null \
+        && $comp -O0 -fopenmp check_omp_v2.f90 \
+	&& echo $(./a.out | grep "Tests:" | cut -d ":" -f2- ) $(echo " : ") $($comp --version | head -n 1) >> $FILE
+
+done
+
+# Display
+cat $FILE
+
diff --git a/scripts/verif_omp/update_comp.sh b/scripts/verif_omp/update_comp.sh
new file mode 100755
index 00000000..14b644de
--- /dev/null
+++ b/scripts/verif_omp/update_comp.sh
@@ -0,0 +1,49 @@
+#!/bin/bash
+
+# Compiler
+COMP=$1
+
+# Path to file.cfg
+config_PATH="../../config/"
+END="*.cfg"
+CONFIG="/config/"
+
+#LIST=${config_PATH}${COMP}${END} # without ${QP_ROOT}
+LIST=${QP_ROOT}${CONFIG}${COMP}${END}
+
+if [ -z "$1" ]
+then
+    echo "Give the compiler in argument"
+else
+
+    # List of the config files for the compiler
+    #list_files=$(ls ../../config/$comp*.cfg) #does not give the right list
+    list_files=${LIST}
+    echo "Files that will be modified:"
+    echo $list_files
+   
+    # Flags that must be added 
+    FLAGS=$(./check_required_setup.sh $COMP)
+
+    # Add the flags
+    for file in $list_files
+    do
+        echo $file
+        BASE="IRPF90_FLAGS : --ninja"
+        ACTUAL=$(grep "$BASE" $file)
+        
+        # To have only one time each flag	
+	grep " -DSET_MAX_ACT" $file && ${ACTUAL/" -DSET_MAX"/""}
+	grep " -DSET_NESTED" $file && ${ACTUAL/" -DSET_NESTED"/""}
+        SPACE=" "
+
+	NEW=${ACTUAL}${SPACE}${FLAGS}
+
+	# Debug
+        #echo ${NEW}
+
+        sed "s/${ACTUAL}/${NEW}/" $file
+        # -i # to change the files
+    done
+
+fi
diff --git a/src/davidson/davidson_parallel.irp.f b/src/davidson/davidson_parallel.irp.f
index 8fd023da..fcee16bc 100644
--- a/src/davidson/davidson_parallel.irp.f
+++ b/src/davidson/davidson_parallel.irp.f
@@ -508,7 +508,8 @@ subroutine H_S2_u_0_nstates_zmq(v_0,s_0,u_0,N_st,sze)
   endif
 
 
-  call omp_set_max_active_levels(5)
+  !call omp_set_max_active_levels(5)
+  call set_multiple_levels_omp()
 
   !$OMP PARALLEL DEFAULT(shared) NUM_THREADS(2) PRIVATE(ithread)
   ithread = omp_get_thread_num()
diff --git a/src/davidson/davidson_parallel_csf.irp.f b/src/davidson/davidson_parallel_csf.irp.f
index fe651b1d..90e4303e 100644
--- a/src/davidson/davidson_parallel_csf.irp.f
+++ b/src/davidson/davidson_parallel_csf.irp.f
@@ -464,7 +464,9 @@ subroutine H_u_0_nstates_zmq(v_0,u_0,N_st,sze)
     print *,  irp_here, ': Failed in zmq_set_running'
   endif
 
-  call omp_set_max_active_levels(4)
+  !call omp_set_max_active_levels(4)
+  call set_multiple_levels_omp()
+
   !$OMP PARALLEL DEFAULT(shared) NUM_THREADS(2) PRIVATE(ithread)
   ithread = omp_get_thread_num()
   if (ithread == 0 ) then
diff --git a/src/davidson/davidson_parallel_nos2.irp.f b/src/davidson/davidson_parallel_nos2.irp.f
index 84cbe3af..091b8666 100644
--- a/src/davidson/davidson_parallel_nos2.irp.f
+++ b/src/davidson/davidson_parallel_nos2.irp.f
@@ -464,7 +464,9 @@ subroutine H_u_0_nstates_zmq(v_0,u_0,N_st,sze)
     print *,  irp_here, ': Failed in zmq_set_running'
   endif
 
-  call omp_set_max_active_levels(4)
+  !call omp_set_max_active_levels(4)
+  call set_multiple_levels_omp()
+
   !$OMP PARALLEL DEFAULT(shared) NUM_THREADS(2) PRIVATE(ithread)
   ithread = omp_get_thread_num()
   if (ithread == 0 ) then
diff --git a/src/fci/check_omp_actual_setup.irp.f b/src/fci/check_omp_actual_setup.irp.f
new file mode 100644
index 00000000..70514bd3
--- /dev/null
+++ b/src/fci/check_omp_actual_setup.irp.f
@@ -0,0 +1,174 @@
+program check_omp_actual_setup
+ 
+  use omp_lib
+
+  implicit none
+
+  integer :: accu, accu2
+  integer :: s, n_setting
+  logical :: verbose, test_versions
+  logical, allocatable :: is_working(:)
+
+  verbose = .True.
+  test_versions = .False.
+  n_setting = 4
+
+  allocate(is_working(n_setting))
+
+  is_working = .False.
+
+  ! set the number of threads
+  call omp_set_num_threads(2) 
+
+  do s = 1, n_setting
+
+    accu = 0
+    accu2 = 0
+
+    call omp_set_max_active_levels(1)
+    call omp_set_nested(.False.)
+
+    if (s==1) then
+      call set_multiple_levels_omp()
+    elseif (s==2) then
+      call omp_set_max_active_levels(5)
+    elseif (s==3) then
+      call omp_set_nested(.True.)
+    else
+      call omp_set_nested(.True.)
+      call omp_set_max_active_levels(5)
+    endif
+
+    ! Level 1
+    !$OMP PARALLEL 
+      if (verbose) then
+        print*,'Num threads level 1:',omp_get_num_threads()
+      endif
+
+      ! Level 2
+      !$OMP PARALLEL 
+        if (verbose) then
+          print*,'Num threads level 2:',omp_get_num_threads()
+        endif
+
+        ! Level 3
+        !$OMP PARALLEL 
+          if (verbose) then
+            print*,'Num threads level 3:',omp_get_num_threads()
+          endif
+
+          call check_omp_in_subroutine(accu2)
+     
+          ! Level 4
+          !$OMP PARALLEL 
+
+            if (verbose) then
+              print*,'Num threads level 4:',omp_get_num_threads()
+            endif
+
+           !$OMP ATOMIC    
+           accu = accu + 1
+           !$OMP END ATOMIC 
+       
+          !$OMP END PARALLEL
+     
+     
+        !$OMP END PARALLEL
+
+
+      !$OMP END PARALLEL
+
+
+    !$OMP END PARALLEL
+
+  if (verbose) then
+    print*,'Setting:',s,'accu=',accu
+    print*,'Setting:',s,'accu2=',accu2
+  endif
+
+  if (accu == 16 .and. accu2 == 16) then
+    is_working(s) = .True.
+  endif
+
+  enddo
+
+  if (verbose) then
+    if (is_working(2)) then
+      print*,'The parallelization works on 4 levels with:'
+      print*,'call omp_set_max_active_levels(5)'
+      print*,''
+      print*,'Please use the irpf90 flags -DSET_MAX_ACT in qp2/config/${compiler_name}.cfg'
+    elseif (is_working(3)) then
+      print*,'The parallelization works on 4 levels with:'
+      print*,'call omp_set_nested(.True.)'
+      print*,''
+      print*,'Please use the irpf90 flag -DSET_NESTED in qp2/config/${compiler_name}.cfg'
+    elseif (is_working(4)) then
+      print*,'The parallelization works on 4 levels with:'
+      print*,'call omp_set_nested(.True.)'
+      print*,'+'
+      print*,'call omp_set_max_active_levels(5)'
+      print*,''
+      print*,'Please use the irpf90 flags -DSET_NESTED -DSET_MAX_ACT in qp2/config/${compiler_name}.cfg'
+    else
+      print*,'The parallelization on multiple levels does not work with:'
+      print*,'call omp_set_max_active_levels(5)'
+      print*,'or'
+      print*,'call omp_set_nested(.True.)'
+      print*,'or'
+      print*,'call omp_set_nested(.True.)'
+      print*,'+'
+      print*,'call omp_set_max_active_levels(5)'
+      print*,''
+      print*,'Try an other compiler and good luck...'
+    endif
+
+    if (is_working(1)) then
+      print*,''
+      print*,'=========================================================='
+      print*,'Your actual set up works for parallelization with 4 levels'
+      print*,'=========================================================='
+      print*,''
+    else
+      print*,''
+      print*,'==================================================================='
+      print*,'Your actual set up does not work for parallelization with 4 levels'
+      print*,'Please look at the previous messages to understand the requirements'
+      print*,'==================================================================='
+      print*,''
+    endif
+  endif
+
+  ! List of working flags
+  if (test_versions) then
+    print*,is_working(2:4)
+  endif
+
+  ! IRPF90_FLAGS
+  if (is_working(2)) then
+    print*,'-DSET_MAX_ACT'
+  elseif (is_working(3)) then
+    print*,'-DSET_NESTED'
+  elseif (is_working(4)) then
+    print*,'-DSET_MAX_ACT -DSET_NESTED'
+  else
+    print*,'ERROR'
+  endif
+
+end
+
+subroutine check_omp_in_subroutine(accu2)
+
+  implicit none
+ 
+  integer, intent(inout) :: accu2
+
+  !$OMP PARALLEL
+
+  !$OMP ATOMIC
+  accu2 = accu2 + 1
+  !$OMP END ATOMIC
+
+  !$OMP END PARALLEL
+
+end
diff --git a/src/utils/set_multiple_levels_omp.irp.f b/src/utils/set_multiple_levels_omp.irp.f
new file mode 100644
index 00000000..4be3af5b
--- /dev/null
+++ b/src/utils/set_multiple_levels_omp.irp.f
@@ -0,0 +1,16 @@
+subroutine set_multiple_levels_omp()
+
+! Doc : idk
+
+  implicit none
+
+  IRP_IF SET_MAX_ACT
+    !print*,'SET_MAX_ACT: True, call omp_set_max_active_levels(5)'
+    call omp_set_max_active_levels(5)
+  IRP_ENDIF
+  IRP_IF SET_NESTED
+    !print*,'SET_NESTED: True, call omp_set_nested(.True.)'
+    call omp_set_nested(.True.)
+  IRP_ENDIF
+
+end