Ab initio simulations of dielectric and optical properties of ices I-=SUB=-h-=/SUB=-, I-=SUB=-II-=/SUB=- and lattices of hydrates sI, sH

Abstract

The results of calculating the dielectric and optical characteristics of solid polymorphic phases of water ices Ih, III and lattices of hydrates sI, sH are presented. Static dielectric tensors εik and complex frequency-dependent tensors εik(ω) are calculated for these materials. It is shown that, in terms of optical properties, the crystal lattices Ih, III, and sH are uniaxial, the tensor components εxx(ω) and εyy(ω) coincide for them, and the hydrate lattice sI is isotropic. Based on the calculated frequency-dependent dielectric functions ε'ik(ω) and ε''ik(ω), important optical characteristics were obtained: reflection R(ω), absorption a(ω), loss function L(ω), refractive indices n(ω) and k(ω). Comparison of the dielectric and optical spectra of the sI and sH gratings with the known spectra for methane hydrate sI revealed a broadening of the spectra in the high-energy direction. For the unfilled hydrate sI, a reflection peak was found at an energy of 17.3 eV, 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 is obtained between the reflection spectra R(ω) and the functions ε'ik(ω), ε''ik(ω), calculated by quantum mechanical simulation, with experimental spectroscopy data for hexagonal and amorphous ices. Keywords: ice, hydrate, dielectric tensor, optical functions.