Theoretical predictions for low-temperature phases, softening of phonons and elastic stiffnesses, and electronic properties of sodium peroxide under high pressure

Abstract

High-pressure phase stabilities up to 600 K and the related properties of Na2O2 under pressures up to 300 GPa were investigated using first-principles calculations and the quasi-harmonic approximation.

Lattice dynamic stability and electronic structures of ternary hydrides La1−xYxH3via first-principles cluster expansion

“…Note that for all our calculations regarding the La 1Àx Y x H 3 alloys, all the corresponding structures are evaluated without taking into consideration the entropy (S) contributions due to the fact that DFT works at 0 K and is capable of determining compounds closely resembling those found in experiment. [40][41][42][43][44][45][46] At this stage, it is worth mentioning once again that at the pressure of 20 GPa, La 0.8 Y 0.2 H 3 , La 0.75 Y 0.25 H 3 , and La 0.5 Y 0.5 H 3 have negative energies of formation relative to those of LaH 3 and YH 3 . Although formation energy suggests thermodynamic stability, it does not suffice to guarantee the existence of such compounds.…”

“…Note that for all our calculations regarding the La 1− x Y x H 3 alloys, all the corresponding structures are evaluated without taking into consideration the entropy ( S ) contributions due to the fact that DFT works at 0 K and is capable of determining compounds closely resembling those found in experiment. 40–46…”

Electronic topological transitions and mechanical properties of hafnium dioxide allotrope at high pressure: Evolutionary first-principles techniques

“…At this point, it should be mentioned that our calculations were performed at a temperature of 0 K, indicating that the enthalpy can confirm a phase stability under high pressure. [16,17,18,19,20,21,22,23] This is due to the fact that there is no entropy contribution. Also, the relationship between pure elements Hf and O indicated the the relative enthalpy of HfO 2 .…”

Semiconducting phase of hafnium dioxide under high pressure: a theoretical studied by quasi-particle GW calculations

“…It should be noted that our calculations were performed at a temperature of 0 K, indicating that the enthalpy can confirm a phase stability under high pressure. [30,31,32,33,34,35,36,37] This is due to the fact that there is no entropy contribution. As a result, the relationship between pure elements Hf and O displayed the formation of HfO 2 .…”