mcscf_calc_energy Subroutine

   subroutine mcscf_calc_energy(this, fragment, result)
      !! Calculate electronic energy using CASSCF
      !!
      !! TODO: Implementation requires:
      !! 1. Build basis set and compute integrals
      !! 2. Initial orbital guess (HF or read from file)
      !! 3. Partition orbitals: inactive, active, virtual
      !! 4. Macro iterations:
      !!    a. Transform integrals to MO basis
      !!    b. Solve CI in active space (Davidson or direct)
      !!    c. Build 1- and 2-RDMs from CI vector
      !!    d. Compute orbital gradient
      !!    e. Update orbitals (super-CI, Newton-Raphson, etc.)
      !!    f. Check convergence
      !! 5. Optional: CASPT2/NEVPT2 correction
      class(mcscf_method_t), intent(in) :: this
      type(physical_fragment_t), intent(in) :: fragment
      type(calculation_result_t), intent(out) :: result

      integer :: n_inactive

      if (this%options%verbose) then
         print *, "MCSCF: Calculating CASSCF energy"
         print *, "MCSCF: Basis set: ", trim(this%options%basis_set)
         print *, "MCSCF: Fragment has", fragment%n_atoms, "atoms"
         print *, "MCSCF: nelec =", fragment%nelec
         print *, "MCSCF: charge =", fragment%charge
         print *, "MCSCF: Active space: (", this%options%n_active_electrons, ",", &
            this%options%n_active_orbitals, ")"

         ! Calculate inactive orbitals
         if (this%options%n_inactive_orbitals < 0) then
            n_inactive = (fragment%nelec - this%options%n_active_electrons)/2
         else
            n_inactive = this%options%n_inactive_orbitals
         end if
         print *, "MCSCF: Inactive orbitals:", n_inactive

         if (this%options%n_states > 1) then
            print *, "MCSCF: State-averaged over", this%options%n_states, "states"
         end if
         if (this%options%use_pt2) then
            print *, "MCSCF: Will apply ", trim(this%options%pt2_type), " correction"
         end if
      end if

      ! Validate active space
      if (this%options%n_active_electrons <= 0 .or. this%options%n_active_orbitals <= 0) then
         print *, "MCSCF: ERROR - Active space not defined!"
         print *, "MCSCF: Set n_active_electrons and n_active_orbitals in config"
         result%has_error = .true.
         return
      end if

      ! Placeholder: Return dummy energy
      ! TODO: Implement actual CASSCF calculation
      result%energy%scf = -1.0_dp*fragment%n_atoms  ! Placeholder
      result%has_energy = .true.

      if (this%options%verbose) then
         print *, "MCSCF: [STUB] CASSCF Energy =", result%energy%total()
      end if

   end subroutine mcscf_calc_energy