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In this paper, theoretical investigations of structural, elastic and thermal properties of Zn3P2 material were done using Quantum ESPRESSO code based on density functional theory. The generalized gradient approximation (GGA) exchange correlation-functional helped to model the atomic interaction. First, the structural optimization procedure was carried out, and hence, the optimized structural parameters were utilized to obtain six independent elastic constants C 1 1 , C 1 2 , C 1 3 , C 3 3 , C 4 4 , and C 6 6 for the Zn3P2 tetragonal structure. Accordingly, these elastic constants were used to determine the elastic moduli such as the Bulk modulus, Young's modulus, and shear modulus, as well as other mechanical parameters such as Pugh's ratio, Poisson's ratio, anisotropic ratio, sound velocities and Debye temperature. Calculations of thermodynamic properties such as vibrational energies, vibrational free energies, and fixed volume heat capacities, were performed within the implementation of the Thermo_pw code. Elastic calculations confirmed that this compound is characterized by mechanical stability at zero pressure and 0K temperature, ionic bonding, a high degree of anisotropy, and typical ductility. An observable increase in Debye vibrational energies, entropies and constant volume heat capacities of this compound with increasing temperature was detected throughout the thermodynamic calculations, unlike vibrational free energy which revealed a pronounced decrease as temperature increased. [ABSTRACT FROM AUTHOR]

In this paper, we studied the magnetic stability, structural, elastic and electronic properties of Ir2FeAl full Heusler compound in the regular phase (Cu2MnAl, prototype L2 1) , by using the first principle of density functional theory, with the generalized approximation of the GGA gradient. We found that the ferromagnetic state of Ir2FeAl is more stable than the nonmagnetic configuration at their lattice parameters equilibrium. This result was confirmed by the calculation of the cohesive energy. The stability is asserted by the elastic constants and the conditions of the mechanical stability criterion. The band structure and the calculated densities of states (DOS) of this alloy show a semi-metallic behavior. The ferromagnetic performance of Ir2FeAl is confirmed by the total magnetic moment of 4.28 μ B , where its major contribution comes from Fe atoms. We estimated the Debye temperature of Ir2FeAl from the average speed of sound. This is the first quantitative theoretical prediction of the elastic properties of the Ir2FeAl compound, and it still awaits experimental confirmation. [ABSTRACT FROM AUTHOR]

In this paper, we have developed models based on Deep-Learning Neural Network (DNN) for accurately predicting lattice constants of half-Heusler alloys. A commercial software WIEN2k employing the Density Functional Theory (DFT) is first used to generate data of the lattice constants of 377 half-Heusler alloys for the training, testing and validation of the models. These models use elemental symbols or/and ionic radii as input parameters. The model that uses only symbols of the constituent element and the model that uses symbols in combination with the radii of the ions predict lattice constants of half-Heusler alloys with an average error of less than 1% to the data obtained from the WIEN2k calculations. The average error stays below 2% in the prediction by the model that uses radii of the ions alone. These results show a great promise for these models to be extended for the prediction of structural and elastic properties of not only new half-Heusler alloys but also other new materials such as full-Heusler, spinels, perovskites, etc. with greater convenience, saving hours of computation time. [ABSTRACT FROM AUTHOR]

In this paper, thermodynamic and elastic properties of the AlNi and AlNi3 were investigated using density functional theory (DFT). The full-potential linearized augmented plane-wave (APW) in the framework of the generalized gradient approximation as used as implemented in the Wien2k package. The temperature dependence of thermal expansion coefficient, bulk modulus and heat capacity in a wide range of temperature (0-1600 K) were investigated. The calculated elastic properties of the compounds show that both intermetallic compounds of AlNi and AlNi3 have surprisingly negative Poisson's ratio (NPR). The results were compared with other experimental and computational data. [ABSTRACT FROM AUTHOR]

In this paper, we employ first-principles methods based on electronic density functional theory (DFT) to investigate the phase stability, elastic and thermodynamic properties of Zr–Al binary substitutional alloys which are Zr3Al, Zr2Al, ZrAl, ZrAl2 and ZrAl3. By analyzing the elastic constants and enthalpy of formation, those phases both satisfy the generalized stability criteria and the results show that ZrAl2 is the most stable. Due to high bulk modulus B, shear modulus G and Youngs modulus Y, ZrAl2 also possesses excellent mechanical properties. Moreover, it is expected that there will be covalent bonding between Zr and Al atom in ZrAl2 compound, which is confirmed by the electronic structure and the differences of charge density discussions. In the end, based on the calculated elastic modulus, the elastic wave velocity, Debye temperature ΘD and specific heat CV are discussed. As a result, ZrAl3 possesses the highest Debye temperature and sound velocity, meaning a larger associated thermal conductivity and higher melting temperature [ABSTRACT FROM AUTHOR]

In this paper, the structural, elastic, electronic and thermodynamic properties of and intermetallic compound are investigated using pseudopotential method based on density functional theory (DFT) under pressure. In this work, the calculated lattice constant and bulk modulus are in accordance with experimental values at zero temperature and zero pressure. The bulk modulus , shear modulus and Young's modulus for and increase with the increasing external pressure. It is noted that of investigated compound has the largest , and . The results of and have the same change trend, but presents an irregular change for and . The density of states for and are investigated at 0, 30 and 50 GPa. In addition, the thermodynamic properties as a function of temperature at different pressure are also studied. [ABSTRACT FROM AUTHOR]

Vacancy plays a crucial role in mechanical properties of transition metal borides (TMBs). However, the influence of vacancy on hardness of TMBs is unknown. In this paper, the relationship between boron vacancy and mechanical properties of CrB4 is investigated by first-principle calculations. Two different vacancies including boron monovacancy (MV) and boron bivacancy (BV) are considered. We find that CrB4 with boron MV is more stable than that of boron BV. The removed atom weakens the deformation resistances, and reduces the elastic stiffness and hardness. The calculated shear modulus, Young's modulus and theoretical hardness of boron MV are larger than that of boron BV. The reason is that the removed atom weakens the localized hybridization between B and B atoms, and damages the 3D-network B-B covalent bond. However, the bulk modulus of B is slightly larger than that of perfect CrB4. This reason is attributed to the formation of triangular pyramid bonding in B vacancy. [ABSTRACT FROM AUTHOR]

The phonon, elastic and thermodynamic properties of L12 phase Rh3Zr have been investigated by density functional theory approach combining with quasi-harmonic approximation model. The relaxed lattice parameters of L12 phase Rh3Zr at zero pressure are in good agreement with the experiment. To judge the stability of L12 phase Rh3Zr under high pressure, the phonon band structure has been studied. The results show that L12 phase Rh3Zr possesses dynamical stability in the pressure range from 0GPa to 80GPa due to the absence of imaginary frequencies. The pressure dependences of elastic constants have been analyzed. All the elastic constants of Rh3Zr in a wide pressure range (0-80GPa) meet general mechanical conditions, suggesting that L12 phase Rh3Zr is mechanically stable under pressure up to 80GPa. L12 phase Rh3Zr exhibits ductility under high pressure and the pressure can improve the ductility from the results of the value of and Poisson's ratio . Hence, it is obvious that the mechanical properties of Rh3Zr can be improved under high pressure. Moreover, we have obtained the thermodynamic properties using the quasi-harmonic Debye model. We note that the effect of the temperature on the Debye temperature is smaller than that of the pressure. We believe that our result will be a good guidance to future works and applications. [ABSTRACT FROM AUTHOR]

The site preference of X (X = Mn, Fe, Co, Cu) in NiAl and its effects on structural, electronic and elastic properties were investigated by performing first-principles calculations using density functional theory (DFT). Formation enthalpy calculations show that adding X increases the formation enthalpy of NiAl, indicating that X addition reduces the stability of system. The site preference was investigated by calculating the transfer energy of NiAl alloys with X. The results further exhibit that Mn, Fe and Cu show no site preference, but Co tends to occupy Ni site. By analyzing electronic density of states, Mulliken population, overlap population and valence charge density, the electronic property and bond characters were discussed. The elastic property calculation shows that only substitution of Ni by Cu increased the plasticity of alloy, while in the other cases the plasticity was decreased. [ABSTRACT FROM AUTHOR]

A comparative study on the structure stability and elastic properties for various types of tungsten tetraboride (4) has been carried out with the generalized gradient approximation (GGA) and local density approximation (LDA) in the framework of density functional theory (DFT). Five types of 4 are considered i.e., orthorhombic Immm, Pnnm, Pmmn, monoclinic C2/m and hexagonal P63/mmc structure. Our calculations indicate that the P63/mmc-4u structure of 4 is unstable at both ambient and pressure conditions, but the other four types of 4 are stable, in agreement with recent theoretical results. By eliminating mechanical calculations, we find that the four types (C2/m, Immm, Pnnm and Pmmn) of 4 are potential candidates to be ultra-incompressible and hard materials. Moreover, the 4 in C2/m type is the most ultra-incompressible among the considered structures due to its superior mechanical properties, and the P63/mmc-2u structure of 4 is not considered to be hard material because of its low hardness. In addition, the calculated B/G ratio exhibits the positive pressure dependence, and four types show brittle nature within 100 GPa. [ABSTRACT FROM AUTHOR]

The elastic and electronic properties of cubic structure CeO2 under pressure are in-vestigated in the frame of density functional theory (DFT). By using the local-density approximation (LDA) plus U (LDA+f/) method with U = 6 eV, the calculated lattice parameters, bulk modulus and elastic properties of the cubic Ce02 at 0 GPa and 0 K are in good agreement with the available experimental data. The pressure dependences of lattice parameters, bulk and shear modulus, Debye temperature, Young's moduli, Poisson's ratio and the compressional and shear wave velocities of the cubic CeO2 are obtained successfully. In addition, the total density of states (TDOS) and the band gaps of the cubic CeO2 under pressures are also investigated. By comparing the results of LDA and LDA+U, both the conventional LDA and the LDA+U methods can be used to describe the structure of the cubic Ce02 due to the electronic localization of 4/-electron in Ce which is not so strong. However, the LDA+t/ approach can obtain a proper shape of the density of electronic states that agrees well with the measured values. [ABSTRACT FROM AUTHOR]

Structural, electronic, elastic and thermodynamic properties of Rh3X(X = Zr, Nb, Ta) intermetallic compounds are investigated in the framework of density functional theory (DFT). The exchange-correlation (XC) potential is treated with the generalized gradient approximation (GGA) and local density approximation (LDA). The computed ground state properties agree well with the available theoretical and experimental values. The elastic constants are obtained by calculating the total energy versus volume conserving strains using Mehl model. The electronic and bonding properties are discussed from the calculations of band structures (BSs), densities of states and electron charge densities. The volume and bulk modulus at high pressure and temperature are investigated. Additionally, thermodynamic properties such as the heat capacity, thermal expansion and Debye temperature at high pressures and temperatures are also analyzed. [ABSTRACT FROM AUTHOR]

The phase transition, elastic and thermodynamic properties of beryllium (Be) have been studied at high pressures by plane-wave ultrasoft pseudopotential density functional theory (DFT) within the generalized gradient approximation (GGA). It is found that the hcp → bcc phase transition of Be occurs at 506 GPa (T = 0 ) and occurs at 1200 K (P = 0 ). The coefficients of linear thermal expansion of the hexagmal close-packed (hcp), bcc and orthorhombic Be have been calculated. The hcp → orthorhombic → bcc phase transitions do not occur in all range of pressures, that is to say, the orthorhombic Be is not an intermediate phase between the hcp and bcc Be. The obtained bulk modulus (B0) are 113.2 GPa (for hcp Be), 113.1 GPa (for bcc Be) and 70.5 GPa (for orthorhombic Be), respectively. [ABSTRACT FROM AUTHOR]

Mechanical properties and the effect of metallic bonding on the hardness of transition-metal nitrides (, and ) compounds are studied using the first-principles calculation. Present results show that these transition-metal nitrides are mechanically stable and the and are ductile, whereas is predicted to be brittle. Moreover, it is found that the high hardness of , and exhibits a remarkable decrease with transition-metal changed from to , and the metallic d-d interactions play important roles on determining the hardness of transition-metal nitrides. [ABSTRACT FROM AUTHOR]