Probing the mechanism of guest-framework bonding interactions through a first-principles study on the structural and electronic properties of type-II clathrate A Si (A = Na, K, Rb; 0 ≤ ≤ 24) under pressure.

The role of noncovalent bonding, including multiatomic interactions (van der Waals-like forces) and ionic characteristics, in the intermetallic clathrate A Si (A = Na, K, Rb; 0 < ≤ 24) is qualitatively discussed. Using the local density approximation (LDA) to density functional theory (DFT), we investigated the effect of different guest filling and pressure parameters on the structural and electronic properties of these materials. In the context of the rigid-band model, we first noted that the competition between van der Waals-like multiatomic interactions and ionicity due to the extent of charge transfer responsible for guest-framework complexes accounts for the nonmonotonic structural response upon guest filling in A Si (0 ≤ ≤ 8), which is in good agreement with previous experimental findings as well as theoretical predictions.