Abstract

The magnetic states and the magnetic anisotropy barrier of a transition metal molecular
complex, dimolybdenum tetraacetate, are investigated via density functional theory (DFT).
Calculations are performed in the gas phase and on a calcite (10.4) bulk insulating surface, using
the Generalized-Gradient Approximation (GGA)-PBE and the Hubbard-corrected DFT + U and
DFT + U + V functionals. The molecular complex (denoted MoMo) contains two central metallic
molybdenum atoms, embedded in a square cage of acetate groups. Recently, MoMo was observed to
form locally regular networks of immobile molecules on calcite (10.4), at room conditions. As this is
the first example of a metal-coordinated molecule strongly anchored to an insulator surface at room
temperature, we explore here its magnetic properties with the aim to understand whether the system
could be assigned features of a single molecule magnet (SMM) and could represent the basis to
realize stable magnetic networks on insulators. After an introductory review on SMMs, we show that,
while the uncorrected GGA-PBE functional stabilizes MoMo in a nonmagnetic state, the DFT + U
and DFT + U + V approaches stabilize an antiferromagnetic ground state and several meta-stable
ferromagnetic and ferrimagnetic states. Importantly, the energy landscape of magnetic states remains
almost unaltered on the insulating surface. Finally, via a noncollinear magnetic formalism and a
newly introduced algorithm, we calculate the magnetic anisotropy barrier, whose value indicates the
stability of the molecule’s magnetic moment.