Cooperative polarisation in ice Ih and the unusual strength of the hydrogen bond

Cooperative polarisation in ice Ih is illustrated in clusters of eight molecules using local density functional calculations where the exchange-correlation functional is a modified Ceperley-Alder expression. These parameter-free total energy calculations support the four-point charge/polarisable point dipole model of Kozack and Jordan and indicate that cooperative polarisation has a profound effect, not simply increasing the cohesive energy, but also making bond breaking disproportionately difficult.