We describe some unsolved problems of current interest; these involve quantum critical points in ferroelectrics and problems which are not amenable to the usual density functional theory, nor to classical Landau free energy approaches (they are kinetically limited), nor even to the Landau-Kittel relationship for domain size (they do not satisfy the assumption of infinite lateral diameter) because they are dominated by finite aperiodic boundary conditions.
Scott, J. F., Schilling, A., Rowley, S. E., & Gregg, J. M. (2015, June 1). Some current problems in perovskite nano-ferroelectrics and multiferroics: Kinetically-limited systems of finite lateral size. Science and Technology of Advanced Materials. Institute of Physics Publishing. https://doi.org/10.1088/1468-6996/16/3/036001