Polonium bulk and surface vibrational dynamics

AbstractCalculations are presented for the bulk phonons and for surface Rayleigh phonons and resonances for Polonium, the only element known to form in the simple cubic lattice. The static stability of this lattice has been confirmed recently by ab initio simulations which yield two bulk elastic constants, c11 and c12. Constitutive equations are derived for the isotropic cubic lattice based upon the Fuchs's method. This permits effectively a numerical evaluation of central potential force constants for Polonium from the ab initio results. Numerical calculations are then made for the material vibration dynamics in the force constant model with the use of the matching method. The numerical applications yield for Polonium the bulk phonon branches along [100], [110], and [111], and the Rayleigh phonons and surface resonances along the [010] direction in an unreconstructed (001) surface. The local vibration densities of states are calculated for bulk and surface sites for this element. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)