Simulations of proton order and disorder in ice Ih

Computer simulations of ice Ih with different proton orientations are presented. Simulations of proton disordered ice are carried out using a Monte Carlo method which samples over proton degree of freedom, allowing for the calculation of the dielectric constant and for the examination of the degree of proton disorder. Simulations are also presented for two proton ordered structures of ice Ih, the ferroelectric Cmc2(1) structure or ice XI and the antiferroelectric Pna2(1) structure. These simulations indicate that a transition to a proton ordered phase occurs at low temperatures (below 80 K). The symmetry of the ordered phase is found to be dependent on the water potential. The stability of the two proton ordered structures is due to a balance of short-ranged interactions which tend to stabilize the Pna2(1) structure and longer-range interactions which stabilize the Cmc2(1) structure. (C) 2005 American Institute of Physics.