Orbital Density Reconstruction for Molecules

The experimental imaging of electronic orbitals has allowed one to gain a fascinating picture of quantum effects. We here show that the energetically high-lying orbitals that are accessible to experimental visualization in general differ, depending on which approach is used to calculate the orbitals. Therefore, orbital imaging faces the fundamental question of which orbitals are the ones that are visualized. Combining angular-resolved photoemission experiments with first-principles calculations, we show that the orbitals from self-interaction-free Kohn-Sham density functional theory are the ones best suited for the orbital-based interpretation of photoemission.

Figure 1

Pentacene HOMO in momentum space. $|\phi (\mathbf{k})|$ was evaluated on a hemisphere of radius $|\mathbf{k}|=2.80{\AA }^{-1}$ Left: HF. Middle: PBE GGA [24]. Right: KS SIC [17].

Figure 2

Top: HOMO of NTCDA from PBE (left), KS SIC (middle), and square root of the ARPES intensity (right). Bottom: HOMO-1 from B3LYP (left), KS SIC (middle), and experiment (right).

Figure 3

(a) Absolute value of the Fourier transforms of PTCDA orbitals: SIC HOMO-1 (bottom left), SIC HOMO-2 (bottom right), normalized superposition of the degenerate SIC HOMO-3 and HOMO-4 (top left), and normalized superposition of the degenerate GGA HOMO-1 and HOMO-2 (top right). (b) Square root of the ARPES intensity at the four indicated binding energies.