DFT Estimation of Exchange Coupling Constant of Cr₈Molecular Ring using the Hybrid Functional B3LYP

Abstract

A study of electronic and magnetic properties of an octametallic chromium-based homonuclear molecule Cr8F8(CO2 − C(CH3)3)16 is presented, using density functional theory (DFT) approach and linearized augmented plane wave (LAPW) method with Perdew, Burke and Ernzerhof (PBE) and Becke 3-term correlation (B3LYP) functionals. The exchange coupling parameters between transition metals ions are extracted, taking into account two dierent (ferro-and antiferromagnetic) spin congurations. The value J = 3.1 meV found for the hybrid B3LYP functional improves signicantly the one obtained for the PBE functional and gives an evidence for the superiority of the former in simulation of molecular nanomgnets. Moreover, the hybrid functional yields excellent spin density localisation, an enhancement of the HOMO-LUMO gaps and the value 2.81µB of magnetic moment at the chromium centre in good agreement with experiment.

Applicability of the DFT Augmented Symmetry Approach to Simulations of the Chromium-based Rings: Cross-validation Using the PBE Functional

“…10. They compare very well with other theoretical predictions found in literature and based on the PBE functional [20,33]. Any difference between our J values is well within standard variation encountered among other DFT estimates [4,8,25,29,[34][35][36][37][38].…”

“…The magnetic moment of 1.6 µ B for nickel is lower from the expected value by almost a third. However, those results are nearly identical to other theoretical values found in literature, including those obtained by the B3LYP functional [4,20,33]. Magnetic moments are strongly localized as is visible on the spin charge density maps shown in Figures 7, 8, 9, 10, 11 and 12.…”

“…9. For Cr 8 they are consistent with those presented in [9,20,25] and vary in a range of 10%. For the heteronuclear derivatives our values are around 6 times larger, but we were unable to find theoretical results for PBE functional apart from the earlier results obtained using the SIESTA package [25] which may not be reliable due to difficulties encountered in choosing the proper pseudopotentials for the Cd and Ni ions as well as to the approximate charge balancing procedure applied.…”

“…The area outside atomic spheres is called interstitial region and all electrons contained in it are described by the plain wave functions. For consistency we use here the same values of the r mt parameters as in our previous study [1,20] which in turn are identical to those chosen elsewhere [9]. They are presented in Tab.…”

“…All the values in units of meV. For reference other theoretical values are given: the data of the FS approach in WIEN2k [20] and NS approach in SIESTA [33]. Experimental values estimated from inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR) are also shown [32,[39][40][41] …”