Clausius-Mosotti at the Nanoscale: Spontaneously Polarized States Professor Philip B. Allen Dept. of Physics and Astronomy, SUNY Stony Brook, and Dept. of Applied Physics and Applied Mathematics, Columbia University The Clausius-Mosotti theorem shows that an infinite and translationally invariant collection of point polarizable molecules has an effective polarizability that is enhanced by the factor (1- relative to the polarizability a of uncoupled dipoles. If is large enough that the denominator vanishes, a spontaneously polarized state can occur. This is the simplest microscopic model of ferroelectricity. In this informal talk I will discuss what happens in some model nanocrystals, and how the Clausius-Mosotti formula evolves when you progress from nanocrystals toward the bulk.