First-principles calculations of structural and thermodynamic properties of β-PbO

We employed ab-initio calculations to investigate the structural and thermodynamic properties of Massicot or orthorhombic phase of PbO named β-PbO using the projector augmented-wave（PAW） method within the generalized gradient approximation（GGA）. The temperature and pressure dependence of bulk modulus, heat capacity at constant pressure and constant volume, entropy, thermal expansion coefficient and Grüneisen parameter were discussed. Accuracy of two different models, the Debye and Debye-Grüneisen which are based on the quasi-harmonic approximation（QHA） for producing thermodynamic properties of material were compared. According to calculation results, these two models can be used to designate thermodynamic properties for β-PbO with sensible accuracy over a wide range of temperatures and pressures, and our work on the properties of this structure will be useful for more deeply understanding various properties of this structure.

First-principles Calculations of Strengthening Compounds in Magnesium Alloy： A General Review

First-principles computation methods play an important role in developing and designing new magnesium alloys.In this article,we present an overview of the first-principles modeling techniques used in recent years to simulate ideal models of the structure of strengthening compounds in Mg alloys.For typical Mg compounds,structural stability,mechanical properties,electronic structure and thermodynamic properties have been discussed.Specifically,the elastic anisotropies of these compounds are examined,which is highly correlated with the possibility of inducing micro-cracks.Furthermore,some heterogeneous nucleation interfaces investigated by first-principles method are reviewed.Some of the theoretical results are compared with available experimental observations.We hope to illustrate that the first-principles computation can help to accelerate the design of new Mg-based materials and the development of materials genome initiative.Remaining problems and future directions in this research field are considered.

Experimental and computational investigations of LaNi(5-x)Alx (x = 0,0.25, 0.5, 0.75 and 1.0) tritium-storage alloys

Although already scientists in recent years have reported some experimental and theoretical results of LaNi-Al series of tritium-storage alloys, several key aspects remain the subject of considerable debate. In an effort to interpret some of these unknowns, we have performed experimental and theoretical investigations for LaNi（5-x）Alx（x = 0, 0.25, 0.5, 0.75 and 1.0） tritium-storage alloys. Firstly, the XRD characterization indicates that the unit cell volumes of LaNi（5-x）Alx increase with Al content in alloys. Secondly, the PCisotherm measurement of LaNi（5-x）Alxalloys shows that their hydrogen absorption/desorption plateau pressures reduce with the increase of Al content while their plateau widths narrow simultaneously. The deuterium absorption/desorption plateaus have a similar trend to hydrogen＇s except for their plateaus being higher than hydrogen＇s. To explain the above experimental findings, a series of calculations based on density functional theory（DFT） and frozen phonon approach have been performed. The results manifest that：（1） the partial substitutions of Al for Ni reduce the hydrogen formation energies of LaNi（5-x）AlxH and the number of available interstitial sites, and therefore lead to the absorption/desorption plateau pressures being reduced and the plateau widths being narrowed down at the same experimental temperatures;（2） the covalent interaction between H and Ni is an important factor for estimating the stability of LaNi（5-x）Alx-H system;（3） since the calculated enthalpy change H is generally more accurate than the calculated entropy change S with respect to the corresponding experimental value for each LaNi（5-x）AlxH（or D）, the curves of H vs. hydrogen storage capacity instead of Van＇t Hoff relation, can be used to predict the experimental plateau pressures of LaNi（5-x）Alx-H（D or T） at a given temperature;（4） the hydrogen isotope effect of LaNi（5-x）Alx-H（D or T） system can be quantitatively described as a linearity relation between ⊿ZPE ＋ ⊿H^（vib） and 1/√mQ（Q = H, D, T）. From the good agreement between the predicted and experimental ln（PH/P0） and ln（PD/P0）, it is deduced that predicting ln（PT/P0） of LaNi（5-x）Alx T is feasible. The procedure of pre-computing and comparing curves of H vs. hydrogen storage capacity proposed in this paper provided an attractive tool to increase the efficiency of experimental alloying design of hydrogen（deuterium or tritium） storage materials.