Spin-one Ising model for ice VII-plastic ice phase transitions.

We propose a spin model compatible with ice VII-plastic ice phase transitions and critical phenomena discovered recently by computer simulations. The Blume-Capel spin-1 Ising model is extended in order to describe the entropic stabilization effect in the plastic ice phase. The model shares the same set of tricritical exponents with simulation, indicating that they are of the same universality class.