Analytical and numerical treatment of the Mott-Hubbard insulator in infinite dimensions

We calculate the density of states in the half-filled Hubbard model on a Bethe lattice with infinite connectivity. Based on our analytical results to second order in t/U, we propose a new ‘Fixed-Energy Exact Diagonalization’ scheme for the numerical study of the Dynamical Mean-Field Theory. Corroborated by results from the Random Dispersion Approximation, we find that the gap opens at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$U_{\rm c}=4.43 \pm 0.05$\end{document}. Moreover, the density of states near the gap increases algebraically as a function of frequency with an exponent \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\alpha=1/2$\end{document} in the insulating phase. We critically examine other analytical and numerical approaches and specify their merits and limitations when applied to the Mott-Hubbard insulator.