  The factors that affect the thermal conductivity of semiconductors is a topic
of great scientific interest, especially in relation to thermoelectrics. Key
developments have been the concept of the phonon-glass-electron-crystal (PGEC)
and the related idea of rattling to achieve this. We use first principles
phonon and thermal conductivity calculations in order to explore the concept of
rattling for stoichiometric ordered half-Heusler compounds. These compounds can
be regarded as filled zinc blende materials, and the filling atom could be
viewed as a rattler if it is weakly bound. We use two simple metrics, one
related to the frequency and the other to bond frustration and anharmonicity.
We find that both measures correlate with thermal conductivity. This suggests
that both may be useful in screening materials for low thermal conductivity.
