Elastic constants and density of states of a molecular-dynamics model of amorphous silicon

Recently we formed a model of amorphous silicon by using a molecular-dynamics calculation with the Stillinger-Weber potential to rapidly cool liquid silicon. We report here on the calculation of the elastic constants of this model of amorphous silicon at two temperatures, 294 and 478 K. The Rayleigh surface-wave velocity of our model is lower than the minimum shear velocity in the crystal by 0.4×${10}^5$ cm/s. The observed Rayleigh surface-wave velocity is 0.5×${10}^5$ cm/s lower than the minimum shear velocity. The Young’s modulus of our model shows a decrease of 3.5×${10}^{11}$ dyn/${\mathrm{cm}}^2$ from the average Young’s modulus in the crystal, which is close to the observed decrease. We also exhibit the density of states for our model of amorphous silicon and compare it to the observed density of states. The main discrepancy is a shift of the high-energy peak to higher frequencies. The molecular-dynamics models of amorphous silicon we form can be of any size, satisfy periodic boundary conditions by construction, and show no memory of the crystalline phase. Our models seem to be as good as or better than the random-network models that have been used previously to study the tetrahedral semiconductors.