  Using first-principles methods we study theoretically the properties of an
individual $\{Fe_4\}$ single-molecule magnet (SMM) attached to metallic leads
in a single-electron transistor geometry. We show that the conductive leads do
not affect the spin ordering and magnetic anisotropy of the neutral SMM. On the
other hand, the leads have a strong effect on the anisotropy of the charged
states of the molecule, which are probed in Coulomb blockade transport.
Furthermore, we demonstrate that an external electric potential, modeling a
gate electrode, can be used to manipulate the magnetic properties of the
system. For a charged molecule, by localizing the extra charge with the gate
voltage closer to the magnetic core, the anisotropy magnitude and spin ordering
converges to the values found for the isolated $\{Fe_4\}$ SMM. We compare these
findings with the results of recent quantum transport experiments in
three-terminal devices.
