The structural properties of ${\mathrm{Ga}}_{\mathit{n}}$${\mathrm{As}}_{\mathit{n}}$, ${\mathrm{Ga}}_{\mathit{n}}$${\mathrm{P}}_{\mathit{n}}$, and ${\mathrm{Al}}_{\mathit{n}}$${\mathrm{As}}_{\mathit{n}}$ clusters, n=2–5, are determined using the Car-Parrinello method. These Iab initioP results show the existence of a critical size for the advent of alternating arrangements of cations and anions in the case of Ga compounds, in agreement with current interpretations of reactivity measurements. The constant presence of severe undercoordination with respect to the bulk is found in agreement with indications from photoabsorption data on InP. The influence of bond ionicity and size mismatch on the structures of the monatomic isoelectronic clusters is clarified. The effects of temperature are also investigated through simulations of hot (melted) clusters.

• Received 12 July 1991

DOI:https://doi.org/10.1103/PhysRevB.45.4203