Correlation effects in the electronic structure of Mn$_4$ molecular   magnet
  We present joint theoretical-experimental study of the correlation effects in the electronic structure of (pyH)$_3$[Mn$_4$O$_3$Cl$_7$(OAc)$_3$]$\cdot$2MeCN molecular magnet (Mn$_4$). Describing the many-body effects by cluster dynamical mean-field theory, we find that Mn$_4$ is predominantly Hubbard insulator with strong electron correlations. The calculated electron gap (1.8 eV) agrees well with the results of optical conductivity measurements, while other methods, which neglect many-body effects or treat them in a simplified manner, do not provide such an agreement. Strong electron correlations in Mn$_4$ may have important implications for possible future applications. 
D. W. Boukhvalov, L. I. Vergara, V. V. Dobrovitski, M. I. Katsnelson,   A. I. Lichtenstein, P. K\"ogerler, J. L. Musfeldt, B...