Effective potentials for simulations of the thermal conductivity of type-I semiconductor clathrate systems

Intermetallic clathrates are promising candidates for thermoelectric applications. For theoretical investigations of their lattice thermal conductivity, effective potentials for silicon- and germanium-based structures have been developed. To stabilize the fourfold coordinated cage framework, angular dependent potentials are necessary. The phononic properties obtained from these potentials are in good agreement with ab initio calculated and experimental data. Molecular dynamics simulations using the Green-Kubo method are used to calculate the thermal conductivity. Type-I clathrate structures with different degrees of complexity have been studied. The influence of the rattling modes of the guest atoms inside the cages is identified as one source of the low thermal conductivity. However, the vacancies in the host framework also reduce the lattice thermal conductivity of clathrate systems. The results are compared to experimental data where available.