anchor.diff:    call bitstring_to_list(ref_bitmask(1,2), occ(1,2), i, N_int)
     
     
  -  ref_bitmask_energy = 0.d0
     mono_elec_ref_bitmask_energy = 0.d0
     kinetic_ref_bitmask_energy   = 0.d0
     nucl_elec_ref_bitmask_energy = 0.d0
     bi_elec_ref_bitmask_energy = 0.d0
     
     do i = 1, elec_beta_num
  -    ref_bitmask_energy += mo_mono_elec_integral(occ(i,1),occ(i,1)) + mo_mono_elec_integral(occ(i,2),occ(i,2))
       kinetic_ref_bitmask_energy += mo_kinetic_integral(occ(i,1),occ(i,1)) + mo_kinetic_integral(occ(i,2),occ(i,2))
       nucl_elec_ref_bitmask_energy += mo_nucl_elec_integral(occ(i,1),occ(i,1)) + mo_nucl_elec_integral(occ(i,2),occ(i,2))
     enddo
   
     do i = elec_beta_num+1,elec_alpha_num
  -    ref_bitmask_energy += mo_mono_elec_integral(occ(i,1),occ(i,1))
       kinetic_ref_bitmask_energy += mo_kinetic_integral(occ(i,1),occ(i,1)) 
       nucl_elec_ref_bitmask_energy += mo_nucl_elec_integral(occ(i,1),occ(i,1)) 
     enddo
  
positive.code:  BEGIN_PROVIDER [ double precision, ref_bitmask_energy ]
  &BEGIN_PROVIDER [ double precision, mono_elec_ref_bitmask_energy ]
  &BEGIN_PROVIDER [ double precision, kinetic_ref_bitmask_energy ]
  &BEGIN_PROVIDER [ double precision, nucl_elec_ref_bitmask_energy ]
  &BEGIN_PROVIDER [ double precision, bi_elec_ref_bitmask_energy ]
  
negative.code:   do j= 1, elec_alpha_num
      do i = j+1, elec_alpha_num
        bi_elec_ref_bitmask_energy += mo_bielec_integral_jj_anti(occ(i,1),occ(j,1))
      enddo
    enddo
    
    do j= 1, elec_beta_num
      do i = j+1, elec_beta_num
        bi_elec_ref_bitmask_energy += mo_bielec_integral_jj_anti(occ(i,2),occ(j,2))
      enddo
      do i= 1, elec_alpha_num
        bi_elec_ref_bitmask_energy += mo_bielec_integral_jj(occ(i,1),occ(j,2))
      enddo
    enddo
    mono_elec_ref_bitmask_energy = kinetic_ref_bitmask_energy +   nucl_elec_ref_bitmask_energy
    
  END_PROVIDER
  
   BEGIN_PROVIDER [ double precision, ref_bitmask_energy ]
    use bitmasks
    implicit none
    BEGIN_DOC
    ! Energy of the reference bitmask used in Slater rules
    END_DOC
    
    integer                        :: occ(N_int*bit_kind_size,2)
    integer                        :: i,j
    double precision               :: ni,nj
    
    call bitstring_to_list(ref_bitmask(1,1), occ(1,1), i, N_int)
    call bitstring_to_list(ref_bitmask(1,2), occ(1,2), i, N_int)
    
    
    ref_bitmask_energy = 0.d0
    
    do j=1,ao_num
     do i=1,ao_num
       ref_bitmask_energy += 0.5d0 * ( &
           (ao_mono_elec_integral(i,j) + Fock_matrix_alpha_ao(i,j) ) *  HF_density_matrix_ao_alpha(i,j) + &
           (ao_mono_elec_integral(i,j) + Fock_matrix_beta_ao (i,j) ) *  HF_density_matrix_ao_beta (i,j) )
     enddo
    enddo
    
  END_PROVIDER
  
  