  We study the optical properties of lowest-energy carbon allotropes in the
infrared, visible and ultra-violet ranges of light in the general gradient
approximation of the density functional theory. In our calculations we used the
all-electron approach as well as the pseudo-potential approximation. In the
infrared range, the complex dielectric functions, infrared and Raman spectra
have been calculated using CRYSTAL14 program. The electronic properties and
energy-dependent dielectric functions in the visible and ultraviolet ranges
have been calculated using VASP program. We have described with a good accuracy
experimentally known optical properties of cubic diamond crystal. Using
obtained set of relevant parameters for calculations, we have predicted optical
constants, dielectric functions and Raman spectra for the lowest-energy
hypothetical carbon allotropes and lonsdaleite.
