First-principles study of the phonon spectrum of ɛ-GaSe

The phonon spectrum and phonon density of states of ?-GaSe layered semiconductor have been studied from the first principles in the linear-response approximation. The elastic constants and acoustic velocities along and across layers have been determined. The study of the equilibrium structure and phonon spectrum of the (0001) surface of ?-GaSe has demonstrated that the volume and surface structural dynamic properties of these crystals differ insignificantly. The calculated frequencies and symmetries of the phonon modes in the center of the Brillouin zone are in good agreement with the experimental data obtained from the Raman scattering and infrared spectra.     

Lattice Dynamics of Bi2Те3 and Vibrational Modes in Raman Scattering of Topological Insulators MnBi2Te4·n(Bi2Te3)

JETP Letters - This work is devoted to the experimental study and symmetry analysis of the Raman-active vibration modes in MnBi2Te4·n(Bi2Te3) van der Waals topological insulators, where n is...     

Ab initio calculation of vibrational spectra of orthorhombic IV–VI layered crystals

Phonon modes of IV–VI semiconductor crystals with the orthorhombic structure of the crystal lattice have been calculated from first principles using the linear response method. The calculations are compared with the results of theoretical calculations available in the literature for some of the crystals and with the experimental data obtained by IR and Raman spectroscopies. Equilibrium lattice parameters and phonon spectra are calculated for all the crystals.     

Self-consistent Green’s function calculation of deep levels of Ge and S vacancies in GeS

The electronic structure of local defects has been considered in terms of the Green’s function theory in the basis set of localized orbitals. Electronic states in the band gap, resonances, and changes in the electron density in a crystal with a defect have been discussed.     

Self-consistent calculations of the electronic structures of deep Sn and S vacancy levels in SnS by the method of green functions

The theory of Green functions and the basis set of localized orbitals were used to consider the electronic structure of local defect-vacancies in SnS. Electronic states in the forbidden band and resonances and antiresonances in SnS crystals with Sn and S vacancies were discussed.     

Calculating the SnS(010) surface electronic structure using the green function method

The electronic structure of the (010) surface in a layered SnS semiconductor terminating with Sn and S atomic planes is calculated by the Green function method. The electronic structure of a perfect crystal is calculated according to the linear combination of atomic orbitals (LCAO) using Slater s-, p-, and d-orbitals. Defect-induced changes in the density of states and the origin and orbital composition of electronic states in the band gap are discussed.     

Ab initio Calculations of Phonon Dispersion in CdGa2S4

Physics of the Solid State - Abstract—The phonon spectrum of CdGa2S4 has been experimentally investigated by Raman spectroscopy and theoretically analyzed using the density functional theory...     

First-principles calculation of the photothreshold of a β-GaS layered crystal

The photothreshold of a β-GaS layered crystal has been calculated as a function of the thickness of the crystal using the first-principles density functional method. The final thickness of the crystal has been simulated using the periodic plate method. Two adjacent crystal plates consisting of several layers are separated by a vacuum gap with a thickness of two layers, which corresponds to the size of the unit cell of the bulk crystal. It has been shown that, in the crystal with more than 10 layers in thickness, the photothreshold almost ceases to depend on the thickness of the crystal.     

Effect of pressure on phonon spectra and elastic properties of orthorhombic GeSe

The pressure dependences of the phonon frequencies of the Brillouin zone center and also the elastic constants of the GeSe compound have been calculated by the density functional theory method using the ABINIT program package. The results have been compared with the available data of theoretical calculations and measurements of the pressure dependences of the Raman frequency. The calculations have demonstrated that the compound undergoes a continuous phase transition from the simple orthorhombic to body-centered orthorhombic lattice at a pressure about 29 GPa.