Determination of the Elastic Properties of Au5Sn and AuSn 
from Ab Initio Calculations
Elastic constants of single-crystal Au5Sn and AuSn were determined through ab␣initio calculations to characterize their polycrystalline elastic behavior and elastic anisotropy. The ideal bulk (K = 127 GPa), shear (G = 28 GPa), and Young’s modulus (E = 78 GPa), as well as Poisson’s ratio (v = 0.398), of Au5Sn were determined using the Voigt–Reuss–Hill method and were very close to the range of experimental results; the values of AuSn were 88 GPa, 15 GPa, 42 GPa, and 0.420, but its ideal Young’s modulus was much smaller than the experimentally obtained values. This unusual discrepancy in the Young’s modulus of AuSn is probably attributed to its extraordinarily high anisotropy in Young’s modulus, with a 95 GPa difference between its maximum and minimum values. Au5Sn exhibits relatively low anisotropy in Young’s modulus with a maximum-minimum difference of 38 GPa.