  The adsorption of iron phthalocyanine (FePc) on the passivated H/Si(111)
surface is explored from first principles. We find that the organic molecule is
predominantly physisorbed with a distance to the surface of $2.6 \pm 0.1$
Angstrom, but also exhibits sizable resonance with the underlying substrate.
This establishes the present system as interesting mixed
covalent-van-der-Waals-bound test case, which we use to compare the impact of
different approaches to van-der-Waals interactions. (Spin-polarized) scanning
tunneling microscopy (SP STM) images are simulated, selectively accessing
different molecular orbitals via the applied bias voltage in the spirit of
scanning tunneling spectroscopy. Comparison with experimental STM images
reveals very good agreement. We find a significant magnetic contrast exceeding
$\pm 1$ Angstrom in the SP STM images for $-2$ and $+1.5$ V. Binding energies
of different (transition metal) atoms in the center of the Pc ring are
presented, which particularly show that Fe is strongly bound in the molecule
(about $9.6$ eV). Finally, we discuss different reactions for subsurface doping
by room-temperature FePc deposition and point out two feasible reactions.
