Accurate magnetic couplings in chromium-based molecular rings from broken-symmetry calculations within density functional theory.

Abstract

We present a comprehensive analysis of magnetic coupling in a group of three popular chromium-based molecular rings - the homo-metallic Cr8 ring and the hetero-metallic Cr7Ni and Cr7Zn molecules. We show conclusively that the broken symmetry approach within density functional theory (DFT), based on suitable conventional or range-separated hybrid functionals, provides a quantitatively reliable tool to extract magnetic exchange coupling parameters in all rings considered, which opens a window for additional applications in molecular magnetism. We further show that a non-empirical model spin Hamiltonian, based on the parameters extracted from DFT, leads to excellent agreement with experimental susceptibility data and energy spectra. Moreover, based on an optimally-tuned range-separated hybrid functional approach, we find that gas-phase gaps of the studied molecular rings are much larger than previously calculated, and discuss the implications of the revised electronic structure to potential applications in molecular spintronics.