A temperature dependent simulation of the x-ray powder spectrum of ice Ih using Metropolis Monte Carlo sampling

Abstract

In this study we simulate the temperature dependence of powder x-ray diffraction for ice Ih using a model ice sample and Metropolis Monte Carlo simulations. We permit the water molecules to interact through the revised central force potentials of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1978)]. The model ice sample is a periodic unit cell possessing 192 water molecules which are arranged in their initial configuration to yield very small point dipole and quadrupole moments [J. Chem. Phys. 78, 5103 (1983) and J. Phys. Chem. 87, 4309 (1983)]. We report the x-ray powder simulations for input temperatures of 100, 200, and 260 K, comparing them with earlier work at 20 K. A full set of the corresponding structure factors is computed for 300 K. The results suggest a monotonic decrease in the logarithm of the diffraction intensities with increasing temperature and an abrupt change between 260–300 K. The drastically decreased values at 300 K are consistent with previous related work [J. Phys. Chem. 87, 4309 (1983)]. The results are compared with the literature on related x-ray measurements [Nature 188, 1144 (1960)]. Here we comment on the qualitatively good comparisons between experiment and simulation, we note quantitative differences between experiment and simulation, and we discuss the differences in light of limitations in both experiment and theory.