Atomic positional disorder, phonon spectrum, and molecular-dynamics simulation of ${\mathrm{Tl}}_2$${\mathrm{CaBa}}_2$${\mathrm{Cu}}_2$${\mathrm{O}}_8$ and ${\mathrm{Tl}}_2$${\mathrm{Ca}}_2$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{10}$

The nature of the atomic positional disorder in the high-temperature superconducting ceramic oxides ${\mathrm{Tl}}_2$${\mathrm{CaBa}}_2$${\mathrm{Cu}}_2$${\mathrm{O}}_8$ (Tl 2:1:2:2) and ${\mathrm{Tl}}_2$${\mathrm{Ca}}_2$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{10}$ (Tl 2:2:2:3) is studied with the help of an ionic-type interatomic potential and molecular-dynamics computer simulations. The pair distribution function and the phonon spectrum are calculated using this model and compared with results of neutron-scattering experiments on Tl 2:1:2:2. Calculated results on the partial pair distribution function, partial phonon density of states, mean square atomic vibrational amplitudes, and lattice specific heat are also presented.