Prediction of Exchange Coupling Constant for Mn12 Molecular Magnet Using Dft+U

Abstract

Abstract. Single-molecule magnets are perspective materials for molecular spintronic applications. Predictions of magnetic coupling in these systems have posed a long standing problem, as calculations of this kind require a balanced description of static and dynamic electron correlation. The large size of these systems limits the choice of theoretical methods used. Two methods feasible to predict the exchange coupling parameters are broken symmetry Density Functional Theory (BSDFT) and DFT with empirical Hubbard U parameter (DFT+U). In this contribution we apply DFT+U to study Mn-based molecular magnets using Vanderbilt Ultrasoft Pseudopotential plane wave DFT method, implemented in Quantum ESPRESSSO code. Unlike most previous studies, we adjust U parameters for both metal and ligand atoms using two dineuclear molecular magnets [

Weak antiferromagnetic coupling in molecular ring is predicted correctly by density functional theory plus Hubbard U

“…This diverse benchmarking set ensured more accurate calibration of the empirical parameters than it was done in our preliminary report. 43 Next, we apply this protocol to study the Mn 12 ͑mda͒ AFM wheel, 44,45 proposed as a molecular element for the quantum computer. The weak coupling between two parts of the wheel made possible the experimental observation of the quantum superposition involving entangled magnetic states that was reported for this system.…”

Predictions of the Spin Configuration in Mn12Molecular Magnets Made Accurate with the Help of HubbardUon the Ligand Atoms

“…The DFT+ U approach was also used for J value calculations for different molecular magnets ,,,,− and organometallic compounds. − The general strategy in DFT+ U is to add the Hubbard U -term for d orbitals on metal atoms. Recently, the use of the Hubbard U -parameter for p orbitals on ligand atoms was found necessary to predict correct spin states in different bimolecular manganese complexes, , including both ferro- and antiferromagnetic couplings, mixed valence compounds, and acetate-bridged complexes. The presence of π-dative bonding in the latter was identified as the reason for delocalization of magnetic orbitals and breakdown of the simple superexchange picture .…”