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

Using a realistic model, the mode Grüneisen parameters $\gamma$ and the temperature dependent coefficient of linear thermal expansion $\alpha \left(T\right)$ are calculated for amorphous silicon. The resulting $\gamma$ 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 $\gamma$ (up to $-31\mathrm{}$), caused by volume-driven internal strain. As a result, the values for $\alpha \left(T\right)$ are lower than those of crystalline silicon and are sample dependent.