dft_calc_energy Subroutine

   subroutine dft_calc_energy(this, fragment, result)
      !! Calculate electronic energy using Kohn-Sham DFT
      !!
      !! TODO: Implementation requires:
      !! 1. Build basis set from fragment geometry
      !! 2. Compute one-electron integrals (S, T, V)
      !! 3. Set up integration grid for XC
      !! 4. Initial density guess (SAD or core Hamiltonian)
      !! 5. SCF iterations:
      !!    a. Build Coulomb matrix J
      !!    b. Evaluate XC energy and potential on grid
      !!    c. Build Fock matrix F = H + J + Vxc
      !!    d. Apply DIIS if enabled
      !!    e. Diagonalize F -> new density
      !!    f. Check convergence
      !! 6. Compute final energy
      class(dft_method_t), intent(in) :: this
      type(physical_fragment_t), intent(in) :: fragment
      type(calculation_result_t), intent(out) :: result

      if (this%options%verbose) then
         print *, "DFT: Calculating energy using ", trim(this%options%functional)
         print *, "DFT: Basis set: ", trim(this%options%basis_set)
         print *, "DFT: Fragment has", fragment%n_atoms, "atoms"
         print *, "DFT: nelec =", fragment%nelec
         print *, "DFT: charge =", fragment%charge
         print *, "DFT: Grid type: ", trim(this%options%grid_type)
         if (this%options%use_density_fitting) then
            print *, "DFT: Using density fitting (RI-J)"
         end if
         if (this%options%use_dispersion) then
            print *, "DFT: Dispersion correction: ", trim(this%options%dispersion_type)
         end if
      end if

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

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

   end subroutine dft_calc_energy