Thermal Expansion and Grüneisen Parameters of Amorphous Silicon: A Realistic Model Calculation

Using a realistic model, the mode Gr\"uneisen parameters γ and the temperature dependent coefficient of linear thermal expansion α(T) are calculated for amorphous silicon. The resulting γ values differ from the crystalline case in having all diversity suppressed, except for a minority of high-frequency localized and low-frequency resonant modes. The latter have very large, mostly negative γ (up to -31), caused by volume-driven internal strain. As a result, the values for α(T) are lower than those of crystalline silicon and are sample dependent.