Structural phase transition of BeTe: an ab initio molecular dynamics study.

Beryllium telluride (BeTe) with cubic zinc-blende (ZB) structure was studied using ab initio constant pressure method under high pressure. The ab initio molecular dynamics (MD) approach for constant pressure was studied and it was found that the first order phase transition occurs from the ZB structure to the nickel arsenide (NiAs) structure. It has been shown that the MD simulation predicts the transition pressure P T more than the value obtained by the static enthalpy and experimental data. The structural pathway reveals MD simulation such as cubic â†’ tetragonal â†’ orthorhombic â†’ monoclinic â†’ orthorhombic â†’ hexagonal, leading the ZB to NiAs phase. The phase transformation is accompanied by a 10% volume drop and at 80 GPa is likely to be around 35 GPa in the experiment. In the present study, our obtained values can be compared with the experimental and theoretical results. Graphical abstract The energy-volume relation and ZB phase for the BeTe.

Pressure-induced phase transition in CrO2.

The ab initio constant pressure molecular dynamics technique and density functional theory with generalized gradient approximation (GGA) was used to study the pressure-induced phase transition of CrO2. The phase transition of the rutile (P42/mnm) to the orthorhombic CaCl2 (Pnnm) structure at 30 GPa was determined successfully in a constant pressure simulation. This phase transition was analyzed from total energy calculations and, from the enthalpy calculation, occurred at around 17 GPa. Structural properties such as bulk modules, lattice parameters and phase transition were compared with experimental results. The phase transition at 12 ± 3 GPa was in good agreement with experimental results, as was the phase transition from the orthorhombic CaCl2 (Pnnm) to the monoclinic (P21/c) structure also found at 35 GPa.

Electronic structure, optical properties and the mechanism of the B3-B8 phase transition of BeSe: insights from hybrid functionals, lattice dynamics and NPH molecular dynamics.

We have investigated the electronic structure and the mechanism of the pressure induced phase transition of beryllium selenide (BeSe) by employing a first-principles pseudopotential method within the framework of density functional theory. Our study demonstrates that use of the hybrid PBE0 functional (PBE stands for Perdew, Burke and Ernzerhof) leads to significant improvement in the band gap calculations, compared to those using either of the common density functionals (local density approximation (LDA) and generalized gradient approximation (GGA)), which severely underestimate the band gap of BeSe. The band gap obtained from the hybrid PBE0 functional shows excellent agreement with available experimental data. A constant-pressure (NPH) first-principles molecular dynamics (FPMD) approach has been adopted to characterize the first-order pressure induced phase transition from the zinc blende (ZB) to the nickel arsenide (NiAs) structure. We have shown that the FPMD simulation overestimates the transition pressure P(T) (compared to static enthalpy and experimental data) due to overpressure in the simulation box. The MD simulation reveals the structural pathway (cubic → orthorhombic → monoclinic → hexagonal), leading from the ZB phase to the NiAs phase. To find an explanation for the phase transition we calculated the vibrational and elastic properties under pressure. Negative Grüneisen parameters were obtained for the transverse acoustic phonon modes at the X and L high symmetry points. However, no mechanical instability or imaginary frequencies were found at pressures near P(T). Thus the transition results from a thermodynamic instability rather than an elastic/dynamical one. We have also calculated the optical properties of both the B3 and B8 phases, such as the real and imaginary parts of the dielectric constant, reflectivity, loss function and refractive index, and compared them with the existing experimental and theoretical data. An abrupt decrease is obtained from the reflectivity spectrum of the NiAs phase at P(T), which is supported from the peaks in the loss function.

Structural phase transition of CdTe: an ab initio study.

A constant pressure ab initio MD technique and density functional theory with a generalized gradient approximation (GGA) was used to study the pressure-induced phase transition in zinc-blende CdTe. We found that CdTe undergoes a structural first-order phase transition to [Formula: see text] (binary ß-tin) tetragonal structure in the constant pressure molecular dynamics simulation at 20 GPa. When the pressure was increased to 50 GPa, the phase of tetragonal structure converted to a new Imm2 orthorhombic structure. These phase transformations were also calculated by using the enthalpy calculations. Transition phases, lattice parameters and bulk properties we attained are comparable with experimental and theoretical data.

Pressure-induced phase transition in wurtzite ZnTe: an ab initio study.

A constant pressure ab initio MD technique and density functional theory with a generalized gradient approximation (GGA) was used to study the pressure-induced phase transition in wurtzite ZnTe. A first-order phase transition from the wurtzite structure to a Cmcm structure was successfully observed in a constant-pressure molecular dynamics simulation. This phase transformation was also analyzed using enthalpy calculations. We also investigated the stability of wurtzite (WZ) and zinc-blende (ZB) phases from energy-volume calculations, and found that both structures show quite similar equations of state and transform into a Cmcm structure at 16 GPa using enthalpy calculations, in agreement with experimental observations. The transition phase, lattice parameters and bulk properties we obtained are comparable with experimental and theoretical data.

Structural phase transition of SnSe under uniaxial stress and hydrostatic pressure: an ab initio study.

We study the structural behavior of SnSe under the hydrostatic pressure using a constant pressure ab initio technique. We find SnSe undergoes a structural second order phase transition from the orthorhombic (Pnma) structure to orthorhombic (Cmcm) structure in the constant pressure simulation at 7 GPa which is in good agreement with the recent experimental study. The Cmcm structure is fivefold coordinated. This phase transition is also analyzed from the total energy calculations. Besides, we study the behavior of SnSe under uniaxial stress.