anchor.diff:          !   sys: system being studied.
           !   dmqmc_in: DMQMC options.
   
  -        use system, only: sys_t, heisenberg
  +        use system, only: sys_t, heisenberg, ueg
           use dmqmc_data, only: dmqmc_in_t
           use calc, only: dmqmc_rdm_r2, doing_dmqmc_calc, dmqmc_full_r2
           use calc, only: dmqmc_staggered_magnetisation, dmqmc_energy_squared, dmqmc_correlation
  +        use calc, only: dmqmc_potential_energy, dmqmc_kinetic_energy, dmqmc_HI_energy
   
           use errors, only: stop_all
           use const, only: depsilon, p
  
positive.code:             call stop_all(this, 'The instantaneous_rdm option must be used in order to calculate the Renyi-2 entropy.')
          if (doing_dmqmc_calc(dmqmc_full_r2) .and. (.not. dmqmc_in%replica_tricks)) &
              call stop_all(this, 'The replica_tricks option must be used in order to calculate the Renyi-2 entropy.')
  
          if (dmqmc_in%all_spin_sectors) then
              if (abs(sys%heisenberg%magnetic_field) > depsilon .or. &
  
negative.code:             if (dmqmc_in%rdm%calc_ground_rdm .or. dmqmc_in%rdm%calc_inst_rdm) &
                  call stop_all(this,'The calculation of reduced density matrices is not supported for this system.')
          end if
          if (.not. sys%system == ueg) then
              if (doing_dmqmc_calc(dmqmc_kinetic_energy)) &
                  call stop_all(this,'The kinetic energy operator is not supported for this system.')
              if (doing_dmqmc_calc(dmqmc_potential_energy)) &
                  call stop_all(this,'The potential energy operator is not supported for this system.')
          end if
  
          if (allocated(dmqmc_in%correlation_sites)) then
              if (size(dmqmc_in%correlation_sites) /= 2) &
  