Navigating at will on the water phase diagram.

Despite the simplicity of its molecular unit, water is a challenging system because of its uniquely rich polymorphism and predicted but yet unconfirmed features. With a novel space of topology-based coordinates that capture changes in the interatomic network, we systematically track transitions among liquid, amorphous, and crystalline forms of the whole water phase diagram, including the challenging task of nucleation of crystals above and below the melting point. Our approach is based on molecular dynamics and enhanced sampling calculation techniques: mechanisms and free-energy surfaces are discussed for the homogeneous crystallisation of water at ambient conditions, and other phase transitions. We stress that our approach is not specific to water and we show that it can be applied to i) structural phase transitions in other materials like alumina ii) precipitation of salts in water.