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Optical properties
Ab initio simulations of dielectric and optical properties of ices I$_{\mathrm{h}}$, I$_{\mathrm{II}}$ and lattices of hydrates sI, sH
M. B. Yunusova,
R. M. Khusnutdinoffab a Kazan (Volga Region) Federal University, Kazan, Russia
b Udmurt Federal Research Center of the Ural Branch of the Russian Academy of Sciences, Izhevsk, Russia
Abstract:
The results of calculating the dielectric and optical characteristics of solid polymorphic phases of water ices I
$_{\mathrm{h}}$, I
$_{\mathrm{II}}$ and lattices of hydrates sI, sH are presented. Static dielectric tensors
$\varepsilon_{ik}$ and complex frequency-dependent tensors
$\varepsilon_{ik}(\omega)$ are calculated for these materials. It is shown that, in terms of optical properties, the crystal lattices I
$_{\mathrm{h}}$, I
$_{\mathrm{II}}$, and sH are uniaxial, the tensor components
$\varepsilon_{xx}(\omega)$ and
$\varepsilon_{yy}(\omega)$ coincide for them, and the hydrate lattice sI is isotropic. Based on the calculated frequency-dependent dielectric functions
$\varepsilon'_{ik}(\omega)$ and
$\varepsilon''_{ik}(\omega)$, important optical characteristics were obtained: reflection
$R(\omega)$, absorption
$a(\omega)$, loss function
$L(\omega)$, refractive indices
$n(\omega)$ and
$k(\omega)$. 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
$R(\omega)$ and the functions
$\varepsilon'_{ik}(\omega)$,
$\varepsilon''_{ik}(\omega)$, calculated by quantum mechanical simulation, with experimental spectroscopy data for hexagonal and amorphous ices.
Keywords:
ice, hydrate, dielectric tensor, optical functions. Received: 02.11.2022
Revised: 16.11.2022
Accepted: 16.11.2022
DOI:
10.21883/FTT.2023.02.54310.515
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