We present the results of a mixed-space approach, based on first-principles calculations, to investigate phonon dispersions and thermal properties of Mg2Si and Mg2Sn, including the bulk modulus, Grüneisen parameter, heat capacity, and Debye temperature. It is shown that good agreements are obtained between the calculated results and available experimental data for both phonon dispersions and thermal properties. The phonon dispersions are accurately calculated compared with experimental data due to the high-quality description of LO–TO splitting and transverse acoustic branches along the Γ-K-X symmetry line. We also calculate the heat capacity CP and Debye temperature of Mg2Si1−xSnx alloys (x = 0.375, 0.5, 0.625, 0.875). The CP values at high temperature range from 0.5 to 0.7 J/g/K and ΘD values at room temperature from 332 to 384 K as the Sn content decreases from 0.875 to 0.375.
