DIFFERENT MODES OF WATER AGGREGATION ON (111) SURFACES OF FLUORITE STRUCTURES

Molecular-dynamics studies of water aggregation on (111) surfaces of BaF2 and CaF2 show that at a critical coverage of about 0.5 monolayer, regular chain and ring patterns develop on BaF2 and CaF2, respectively, governed by the free energy of the system. At one monolayer, the structure on CaF2 randomizes, whereas on BaF2 it forms a 2D two-dimensional pattern, commensurate with the substrate F- sublattice. Beyond one bilayer, regular ice-Ih grows on BaF2, stable even at room temperature. Vibrational frequencies at low coverages and LEED patterns for high coverages are predicted.