Computer simulation of nanomagnets tethered to gold surfaces

Much of the experimental work aimed at singleelectron devices relies on successfully tethering functional molecules onto gold surfaces. The [Mn12O12(CH3COO)16(H2O)4] molecular nanomagnet has been shown to exhibit an interesting and measurable magnetic signature. Moreover the magnetic behavior has been shown to be very sensitive to changes in charge state and hydrogen-bonding to neighboring molecules. Recent experiments have revealed that the acetate ligands can be successfully substituted by long thiol terminated alkane chains such as C10H20 followed by subsequent attachment to a gold surface. As such we have performed calculations to determine whether the electronic structure and primary magnetic signatures of a molecular magnet can be retained upon attachment. In order to perform these calculations we have used both fine-grained and coarse-grained strategies for determining the geometrical, electronic, and magnetic behavior of these systems. The molecular system has been broken up into three separate fragments that have been separately optimized on the IBM HPC platforms at the NAVO and ARL MSRCs. Further, each fragment calculation employs the massively parallel NRLMOL program to efficiently perform density-functional calculations. The fragments are then reconnected and further optimized prior to determining the magnetic structure. We find that the HOMO-LUMO gap for minority spins decrease dramatically up to 1 eV and that the transverse magnetic anisotropy parameter is induced and the uniaxial magnetic anisotropy of the Mn12 molecule is almost the same as before attachment.