Ab Initio Simulation of Dielectric and Optical Properties of Ices Ih and III and Lattice Frameworks of Hydrates sI and sH

In this study, the results of calculating the dielectric and optical characteristics of solid polymorphic phases of water-namely, ices I-h and I-II, and lattice frameworks of hydrates sI and sH-are described. Static dielectric tensors eik and complex frequency-dependent tensors epsilon(ik)(omega) are calculated for these materials. It is shown that the lattices of I-h, I-II, and sH correspond to uniaxial crystals according to their optical properties, their epsilon(xx)(omega) and epsilon(yy)(omega) tensor components are identical, and the lattice of hydrate sI corresponds to an isotropic crystal. Based on calculated frequency-dependent dielectric functions epsilon(ik) (omega) and epsilon()(ik) (omega), the following important optical characteristics are obtained: reflection R(omega), absorption alpha(omega), loss function L(omega), and refractive indices n(omega) and k(omega). Comparison of the dielectric and optical spectra of the sI and sH lattice frameworks with the known spectra for methane hydrate sI reveal a broadening of the spectra toward high-energy fields. For unfilled hydrate sI, a reflection peak at an energy of 17.3 eV is found, the appearance of which is associated with a change in the electronic structure of the crystal in the absence of a methane molecule. Qualitative agreement of reflection spectra R(omega) and the epsilon(')(ik) (omega) and epsilon()(ik) (omega) functions calculated by quantum mechanical simulation with experimental data on the spectroscopy of the hexagonal and amor-

Automated summary

This study describes the calculation results of the dielectric and optical characteristics of solid polymorphic phases of water, including ices I-h and I-II as well as lattice frameworks of hydrates sI and sH. The dielectric and optical properties of these materials were obtained by calculating the static dielectric tensors and complex frequency-dependent tensors. Important optical characteristics such as reflection, absorption, loss function, and refractive indices were obtained based on the calculated frequency-dependent dielectric functions. A comparison of the dielectric and optical spectra revealed differences between sI and sH lattice frameworks and methane hydrate sI. The results of quantum mechanical simulation showed qualitative agreement with experimental data.