Proton strings and rings in atypical nucleation of ferroelectricity in ice

J. LASAVE; S. KOVAL; A. LAIO; E. TOSATTI

Conferencia; American Physical Society (APS) March Meeting 2021; 2021

Ordinary ice has a proton-disordered phase which is kinetically metastable. Upon doping with KOH at low temperature the transition to ferroelectric (FE) icetakes place, with a mechanism that needs clarification. We introduce a lattice model based on dipolar interactions plus a frustrating term that enforces the icerule (IR). In the absence of IR-breaking defects, standard Monte Carlo (MC) simulations leave the defect-free ice model in a state of disordered proton ringconfigurations with the correct Pauling entropy. A replica-exchange accelerated MC sampling enables full equilibration, reaching low-temperature FE orderthrough a well defined first order phase transition. When proton vacancies mimicking the KOH impurities are planted into this IR-conserving lattice, theyenable standard MC to work, revealing the kinetics of evolution of ice from proton disorder to partial FE order below the transition temperature. Replacingordinary nucleation, each impurity opens up a proton ring generating a linear string, an actual ferroelectric hydrogen-bond wire that expands with time. Thepredicted dependence of FE order fraction upon dopant concentration and quenching temperature agree well with that of real KOH doped ice.