  We describe a classical thermodynamic model that reproduces the main features
of the solid hydrogen phase diagram. In particular, we show how the general
structure types that are found by electronic structure calculations and the
quantum nature of the protons can also be understood from a classical
viewpoint. The model provides a picture not only of crystal structure, but also
for the anomalous melting curve and insights into isotope effects, liquid
metallisation and InfraRed activity. The existence of a classical picture for
this most quantum of condensed matter systems provides a surprising extension
of the correspondence principle of quantum mechanics, in particular the
equivalent effects of classical and quantum uncertainty.
