Characterization of the High-Pressure Structural Transition and Thermodynamic Properties in Sodium Chloride: A Computational Investigation on the Basis of the Density Functional Theory

Abstract

Using first-principles calculations, the elastic constants, the thermodynamic properties, and the structural phase transition between the B1 (rocksalt) and the B2 (cesium chloride) phases of NaCl are investigated by means of the pseudopotential plane-waves method. The calculations are performed within the generalized gradient approximation to density functional theory with the Perdew-Burke-Ernzerhof exchange-correlation functional. On the basis of the third-order Birch-Murnaghan equation of states, the transition pressure Pt between the B1 phase and the B2 phase of NaCl is determined. The calculated values are generally speaking in good agreement with experiments and with similar theoretical calculations. From the theoretical calculations, the shear modulus, Young's modulus, rigidity modulus, and Poisson's ratio of NaCl are derived. According to the quasi-harmonic Debye model, we estimated the Debye temperature of NaCl from the average sound velocity. Moreover, the pressure derivatives of elastic constants, partial differentialC11/partial differentialP, partial differentialC12/partial differentialP, partial differentialC44/partial differentialP, partial differentialS11/partial differential P, partial differentialS12/partial differentialP, and partial differentialS44/partial differentialP, for NaCl crystal are investigated for the first time. This is a quantitative theoretical prediction of the elastic and thermodynamic properties of NaCl, and it still awaits experimental confirmation.

High-pressure structures and metallization of sodium chloride

“…2. It is clearly seen that our calculation correctly predicts the cF8 → cP2 transition at 25 GPa, in good agreement with experiments [8,34,35] and earlier theoretical calculations [2,36,37], validating our methodology in the application to NaCl. Here, the cP2 structure is stable up to 322 GPa, above which the oC8 and oI8 structures become favorable and stable in the pressure ranges 322-645 GPa and 645-683 GPa, respectively.…”

“…Sodium chloride (NaCl), also known as salt, is one of the most widely used colorless nonmetallic mineral materials. It plays a very important role in biology, chemistry, and several other scientific disciplines as well as being an absolutely necessary material for human life, equal in importance to water [1,2]. Many ionic solids (e.g., alkali halides, alkali hydrides, etc.)…”

Activation energy of the low-load NaCl transition from nanoindentation loading curves

“…The normalization per µN load leaves Equation insensitive to creep‐on‐load, so that W trans values can be calculated for every load and temperature of interest. We note here, that published bulk‐ and Young's‐modulus calculations for hydrostatic pressure conditions in diamond pressure cells are “in good agreement with experiments.” The moduli increase strongly for B1‐NaCl with increasing pressure, and further so but less‐steeply for B2‐NaCl after the phase transition (Lu et al ., ) (see Physical Background section). However, in situ diffraction experiments wait for final decision about the type of transition under the Berkovich indenter.…”

“…The hydrostatic transformation pressure upon isothermal compression of five research groups varies from 28.2 to 30.6 GPa with the preferred value at 29.2 GPa (Piermarini and Block, ) or 26.8 GPa (Li and Jeanloz, ). The hydrostatic transformation pressure has been amply theoretically calculated (Lu et al ., ). The higher transition from the CsCl‐type structure of NaCl to the layered CrB‐type structure (space group Cmcm ) of sodium chloride would occur from 322 GPa hydrostatic pressures on (Chen and Ma, ).…”

“…It was obtained at “quasi‐hydrostatic” conditions (with laser annealing) in diamond anvil cells and by using the modified third‐order Birch–Murnaghan equation of states (EOS) or the modified universal EOS (Sata et al ., ). The strong increase of the B2‐bulk modulus from 30 GPa pressure to 70 GPa pressure was obtained from first principle calculations on the basis of density functional theory (139.445 and 270.391 GPa, respectively), and similar calculations of Young's modulus gave 217.880 and 344.963 GPa for 30 and 70 GPa, respectively (Lu et al ., ). Fei et al .…”