Geometry and magnetic structure variation in manganese - oxide clusters determined by a self - consistent , LCAO method

Submitted for the MAR13 Meeting of The American Physical Society Geometry and magnetic structure variation in manganese-oxide clusters determined by a self-consistent, LCAO method1 KRISTEN WILLIAMS, US Army Research Lab, Aberdeen Proving Ground, MD 21005, JOSEPH HOOPER, Dept. of Physics, Naval Postgraduate School, Monterey, CA 93943 — Ab initio simulations are used to study the variation in geometry and magnetic structure in MnxOy (x =3,4; y =1,2) clusters. The groundstate wavefunctions for clusters with different magnetic coupling (ferromagnetic, ferrimagnetic and antiferromagnetic) are modeled with linear combinations of atomic orbitals (LCAOs). Self-consistent energies for different spin isomers are calculated by constraining the magnetic moments of Mn atoms constituting each basis AO. The ferrimagnetic and antiferromagnetic ground-state structures of MnxOy are 0.16–1.20 eV lower in energy than their ferromagnetic isomers. The presence of oxygen thus stabilizes low-spin isomers relative to the preferred high-spin ordering of bare Mn3 and Mn4. Each cluster has a preferred overall magnetic moment, and no evidence is seen of competing states with different spin multiplicities. However, non-degenerate isomags (clusters that possess the same spin multiplicity but different arrangements of local moments) do contribute to peak broadening observed in negative-ion photoelectron spectra. Proper accounting for all possible isomags is shown to be critical for accurate comparison with experimental spectra. 1Research was conducted at Naval Surface Warfare Center, Indian Head, MD and supported by the ONR NREIP program. Kristen Williams US Army Research Lab Aberdeen Date submitted: 15 Nov 2012 Electronic form version 1.4