Elastic properties of glasses.

It is believed that covalent glasses can be divided into two classes: those with high average coordination (amorphous solids) and those with low average coordination (polymeric glasses). We present the first conclusive evidence that this division is correct by calculating the elastic properties of random networks with different average coordination $〈r〉$. The results show that the elastic constants depend predominantly on $〈r〉$ and go to zero when $〈r〉=2.4$ with an exponent $f=1.5\ifmmode\pm\else\textpm\fi{}0.2$.