  Structural and optoelectronic properties of {\alpha}, \{beta}, {\gamma}
phases of calcium titanate are studied with the implementation of
first-principles quantum-chemical calculations in the framework of DFT. When
optimizing the geometry, the GGA approximation was used. The relaxed lattice
parameters obtained by us are identical with the experimental analogs. It has
been established that the most stable phase of calcium titanate is the
orthorhombic syngony, which corresponds to the results of experimental
measurements. It is shown that as the transition from the {\alpha}-phase to the
{\gamma}-phase proceeds, the lattice constant parameters and the interatomic
distance in these systems increase. The optoelectronic properties of these
materials have been studied using the Wien2k code. The high-precision TB-mBJ
approximation was used to calculate the exchange-correlation effects. An
analysis of the electronic properties of these materials showed that all the
studied phases of calcium titanate belong to the class of wide-gap
semiconductors. The calculated band gaps for the cubic, tetragonal, and
orthorhombic CaTiO3 systems are 2.83, 3.07, and 3.26 eV, respectively.
According to the analysis of DOS-plots, it was found that the tetragonal phase
of calcium titanate is characterized by the highest density of states.
Calculations of the optical constants of the systems under study showed that
the CaTiO3 cubic system is characterized by an increased absorption capacity
and a relatively high photoconductivity. However, for the other two phases of
calcium titanate, the calculations gave identical patterns, i.e., the
absorption and optical conductivity spectra of the tetragonal and orthorhombic
CaTiO3 systems practically coincide.
