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