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The structural stability of chromium nitride (CrN) and manganese nitride (MnN) is investigated among four different structures, namely, NaCl (Fm3m), zinc blende (F4-3m), orthorhombic (Pnma) and tetragonal (I4/mmm). It is found that the most stable phase is the zinc blende phase for CrN and MnN. The structural phase transition from zinc blende to orthorhombic phase is predicted at high pressure. At normal pressure, CrN and MnN are found to be antiferromagnetic. As the pressure is increased, antiferromagnetic-to-nonmagnetic phase transition is observed at the pressures of 169.5 GPa in CrN and 206 GPa in MnN. The elastic constants obey the Born--Huang criteria, suggesting that they are mechanically stable. The calculatedB/Gvalues indicate that CrN and MnN are ductile in nature. [ABSTRACT FROM PUBLISHER]

The high-pressure structural phase transition, electronic, superconducting and elastic properties of group III nitrides (ScN, YN and LaN) are investigated by first principles calculation with the density functional theory. The calculated lattice parameters are in good agreement with the experimental and other theoretical values. Electronic structure reveals that these materials are semiconductors with an indirect band gap of 1.4, 0.87 and 0.65 eV for ScN, YN and LaN, respectively. The obtained cubic NaCl structure is energetically the most stable structure at ambient pressure. A pressure-induced structural phase transition from NaCl to CsCl structure is predicted. The structural phase transition of ScN, YN and LaN occurs at a pressure of 158, 132 and 26.5 GPa, respectively. On further increase in the pressure, semiconductor-to-metallic transition and superconductivity is observed in these nitrides. The estimatedTcvalues as a function of pressure for ScN, YN and LaN are 31.79, 15.50 and 12.84 K, respectively. [ABSTRACT FROM PUBLISHER]

The structural, electronic, elastic and magnetic properties of gadolinium and its hydrides GdH x ( x =1, 2, 3) are investigated by using Vienna ab-initio simulation package with the generalized gradient approximation parameterized by Perdew, Burke and Ernzerhof (GGA-PBE) plus a Hubbard parameter (GGA-PBE+ U ) in order to include the strong Coulomb correlation between localized Gd 4f electrons. At ambient pressure all the hydrides are stable in the ferromagnetic state. The calculated lattice parameters are in good agreement with the experimental results. The bulk modulus is found to decrease with the increase in the hydrogen content for the gadolinium hydrides. A pressure-induced structural phase transition is predicted to occur from cubic to hexagonal phase in GdH and GdH 2 and from hexagonal to cubic phase in GdH 3 . The electronic structure reveals that mono and di-hydrides are metallic, whereas trihydride is half-metallic at normal pressure. On further increasing the pressure, a half-metallic to metallic transition is also observed in GdH 3 . The calculated magnetic moment values of GdH x ( x =1, 2, 3) are in accord with the experimental values. [ABSTRACT FROM AUTHOR]

Abstract: The structural, electronic, elastic and magnetic properties of three rare earth nitrides (RENs: RE=Gd, Dy, Ho) are investigated by first principles calculation using Vienna ab-initio simulation code (VASP). At ambient pressure all the three nitrides are stable in the ferromagnetic state (FM) with cubic NaCl(B1) structure. The calculated lattice parameters are in good agreement with experimental and other theoretical values. Electronic structure reveals that these materials are half metallic ferromagnets at normal pressure. A pressure induced structural phase transition from NaCl to wurtzite phase in GdN at 18.2GPa and from NaCl to CsCl phase in DyN at 104GPa and HoN at 138GPa is also predicted. The half metallicity has been retained in GdN, DyN and HoN even after the phase transition but it vanishes at 73.18GPa, 118GPa and 141GPa respectively. Ferromagnetism is quenched in all the three nitrides at a pressure of 252GPa (GdN), 242GPa (DyN) and 236.7GPa (HoN). [Copyright &y& Elsevier]

Abstract: The electronic, structural, mechanical and superconducting properties of group VB mononitrides are investigated by means of first principles calculation based on density functional theory with generalized gradient approximation. The calculated ground state properties are in good agreement with previous experimental and theoretical results. Among the three crystallographic structures that have been investigated, the hexagonal WC phase is found to more stable than the cubic ones. Under high pressure, a series of structural phase transition from WC → NaCl → CsCl phase is also predicted in VN, NbN and TaN. The calculated elastic constants indicate that all the three nitrides are mechanically stable at ambient pressure. The estimated Zener ratio and linear compressibility coefficients K c /K a reveals that these materials exhibit elastic anisotropy. The estimated superconducting transition temperature (T c ) values as a function of pressure for VN, NbN and TaN are 35.5, 37.5 and 30.5 K respectively. [Copyright &y& Elsevier]

Abstract: First-principles calculation was performed using tight-binding LMTO method with local density approximation (LDA) and atomic sphere approximation (ASA) to understand the electronic properties of rhenium nitride. The equilibrium geometries, the electronic band structure, the total and partial DOS are obtained under various pressures and are analyzed in comparison with the available experimental data. The most stable structure of ReN is NiAs like structure. Our results indicate that ReN can be used as a super-hard conductor. We estimated the average electron–phonon coupling constant to be 1.65 and superconducting transition temperature (T c) is 5.1K. The T c value increases with the increase in pressure. [Copyright &y& Elsevier]

Abstract: First principles calculation was performed using tight-binding LMTO method with local density approximation (LDA) and atomic sphere approximation (ASA) to understand the electronic properties of chromium nitride. The equilibrium geometries, the magnetic moment, the electronic band structure, the total and partial DOS are obtained under various pressures and are analyzed in comparison with the available experimental data. The most stable structure of CrN is NaCl structure in the FM state. A pressure-induced second order magnetic phase transition from ferromagnetic (FM) to non-magnetic (NM) at very high pressure of 0.5549Mbar is predicted. Our results indicate that CrN can be used as a hydrogen storage material. [Copyright &y& Elsevier]

The electronic, structural, mechanical and magnetic properties of Actinide nitrides AnN (An = U, Np and Pu) are investigated in three cubic phases, namely, NaCl (B1), CsCl (B2) and zinc blende (B3). At normal pressure, UN is stable in antiferromagnetic state while the other two nitrides are stable in the ferromagnetic state with NaCl (B1) structure. A pressure induced structural phase transition from B1 to B3 phase is predicted in these nitrides. The electronic structure reveals that these nitrides are metallic in nature. The magnetic phase transition from antiferromagnetic to non-magnetic state is observed in UN at a pressure of 127 GPa while ferromagnetic to non-magnetic state is observed in NpN and PuN at the pressures of 67 GPa and 102.3 GPa respectively. The computed structural parameters, bulk modulus density of states and charge density distributions are compared with experimental and other theoretical calculations. [ABSTRACT FROM AUTHOR]

The structural stability of rare earth nitrides REN (RE=Ce,Pr,Nd) is investigated among three cubic structures, namely, NaCl (B1), CsCl(B2) and zinc blende (B3). It is found that NaCl structure is the most stable structure for all the three nitrides. On increasing the pressure, structural phase transition from NaCl (B1) to CsCl (B2) phase is predicted in CeN and NdN at the pressures of 88 GPa and 36.5 GPa while NaCl (B1) to zinc blende (B3) phase transition is observed in PrN at the pressure of 68 GPa. At normal pressure, all the three nitrides are stable in the ferromagnetic state (FM) with cubic NaCl (B1) structure. The calculated lattice parameters and bulk modulus values are in good agreement with experimental and other theoretical values. Electronic structure reveals that PrN and NdN are half metallic while CeN is metallic at normal pressure. Ferromagnetism is quenched in CeN and PrN at the pressures of 152 GPa and 121 GPa respectively. The positive values of elastic constants indicate that all the three nitrides are mechanically stable in NaCl Phase. It is found that all these nitrides are ductile and anisotropic in nature. [ABSTRACT FROM AUTHOR]

The structural, electronic, mechanical and superconducting properties of rhenium carbide (ReC) and technetium carbide (TcC) are investigated using first principles calculations based on density functional theory (DFT). The computed ground state properties like equilibrium lattice constants and cell volume are in good agreement with the available experimental and theoretical data. It is observed that tungsten carbide phase (WC) is the most stable phase for ReC and TcC at normal pressure. Pressure induced structural phase transitions are observed from tungsten carbide to zinc blende phase and then zinc blende to wurtzite phase in rhenium carbide while tungsten carbide to zinc blende phase and then zinc blende to nickel arsenide phase in technetium carbide. Electronic structure reveals that these materials are metallic at ambient condition. The high bulk modulus (B) value of WC phase of both ReC (438 GPa) and TcC (368 GPa) suggests that they are ultra hard and incompressible materials. Also, the superconducting transition temperature is estimated for ReC and TcC at normal pressure. [ABSTRACT FROM AUTHOR]

The structural, electronic, mechanical and superconducting properties of tungsten carbide (WC) and tungsten nitride (WN) are investigated using first principles calculations based on density functional theory (DFT). The computed ground state properties, such as equilibrium lattice constant and cell volume, are in good agreement with the available experimental data. A pressure induced structural phase transition is observed in both tungsten carbide and nitride, from a tungsten carbide phase (WC) to a zinc blende phase (ZB), and from a zinc blende phase (ZB) to a wurtzite phase (WZ). The electronic structure reveals that these materials are metallic at ambient conditions. The calculated elastic constants obey the Born-Huang criteria, suggesting that they are mechanically stable at normal and high pressure. Also, the superconducting transition temperature is estimated for the WC and WN in stable structures at atmospheric pressure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Electronic, structural and elastic properties of alkali hydrides are investigated. [•] A pressure induced structural phase transition is predicted under high pressure. [•] Electronic structure reveals that these materials exhibit non-metallic behavior. [•] Computed elastic moduli obey traditional mechanical stability condition. [•] The Debye temperature values are computed for alkali hydrides. [ABSTRACT FROM AUTHOR]

Highlights: [•] Electronic, structural and elastic properties of group IB nitrides are investigated. [•] A pressure induced structural phase transition is predicted under high pressure. [•] Electronic structure reveals that these materials exhibit metallic behavior. [•] Computed elastic moduli obey traditional mechanical stability condition. [•] The Debye temperature values are computed for Group IB metal mono and di-nitrides. [ABSTRACT FROM AUTHOR]

Abstract: The structural, electronic, mechanical and magnetic properties of 3 alkaline-earth metal nitrides (XN: X=Ca, Sr, and Ba) are investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation code. At ambient pressure all the 3 nitrides are stable in the ferromagnetic state with a cubic NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that these materials are half metallic ferromagnets at normal pressure. A pressure-induced structural phase transition from NaCl (B1) to CsCl (B2) phase is observed in CaN, SrN and BaN. On further increasing the pressure, a half metallic to metallic transition is also observed in these nitrides. Ferromagnetism is quenched in all the 3 nitrides at high pressures. [Copyright &y& Elsevier]

Abstract: First principles calculation were performed using Vienna ab-initio simulation package within the frame work of density functional theory (DFT) to understand the electronic properties of magnesium hydride. At normal pressure, the most stable structure of MgH2 is rutile type with a wide band gap of 3.52eV, which agrees well with the available data. A pressure induced semi-conductor to metallic transition at a pressure of 92.54GPa is predicted. Our results indicate a sequence of pressure induced structural phase transition in MgH2. The obtained sequence of phase transition was α→γ→β→δ→ε at a pressure of 0.37GPa, 3.89GPa,7.23GPa and 11.26GPa, respectively. Thus our results indicate that MgH2 is one of the best hydrogen storage material and the maximum storage capacity achieved was 7.7%. [Copyright &y& Elsevier]