|
|
Ab-initio calculation of structures´ stability of Ni-N compounds
Šárfy, Pavlína ; Vřešťál,, Jan (referee) ; Šob,, Mojmír (advisor)
The present thesis is devoted to ab initio study of electronic structure of nickel nitrides NiN, Ni2N, Ni3N and Ni4N. The results are used to predict the most stable structures for each composition. The total energies and the electronic structures are calculated by means of the pseudopotential method implemented in the Abinit code and by full-potential linearized augmented plane wave (FLAPW) method incorporated in the Wien2K code. For the exchange-correlation energy, both the local density approximation (LDA) and generalized approximation (GGA) are employed. We predicted the face centered cubic structure B3 as the most stable modification of NiN, the primitive tetragonal structure C4 as the most stable modification of Ni2N, the hexagonal structure as the most stable modification of Ni3N (in agreement with experimental data) and the primitive cubic structure as the most stable modification of Ni4N.
|
|
|
Ab-initio calculation of structures´ stability of Ni-N compounds
Šárfy, Pavlína ; Vřešťál,, Jan (referee) ; Šob,, Mojmír (advisor)
The present thesis is devoted to ab initio study of electronic structure of nickel nitrides NiN, Ni2N, Ni3N and Ni4N. The results are used to predict the most stable structures for each composition. The total energies and the electronic structures are calculated by means of the pseudopotential method implemented in the Abinit code and by full-potential linearized augmented plane wave (FLAPW) method incorporated in the Wien2K code. For the exchange-correlation energy, both the local density approximation (LDA) and generalized approximation (GGA) are employed. We predicted the face centered cubic structure B3 as the most stable modification of NiN, the primitive tetragonal structure C4 as the most stable modification of Ni2N, the hexagonal structure as the most stable modification of Ni3N (in agreement with experimental data) and the primitive cubic structure as the most stable modification of Ni4N.
|
|
|
Qantum-mechanical study of structural stability of Ni4N allotropes
Hemzalová, P. ; Friák, Martin ; Šob, Mojmír ; Neugebauer, J.
Parameter-free density functional theory (DFT) calculations of Ni4N in eight crystallographic phases were performed using the pseudopotential approach implemented in the VASP code; the exchange-correlation energy was evaluated within the generalized gradient approximation (GGA). In agreement with experiments, the cubic structure with Pearson symbol cP5, space group Pm-3m (221), has been found to be the most stable. It is also the only thermodynamically stable structure at T=0 K with respect to decomposition into elemental Ni crystal and N2 gas phase. We determine structural, thermodynamic, electronic, magnetic and elastic properties of all eight Ni4N allotropes studied. The thermodynamic stability and bulk modulus is found to be anti-correlated. For the cubic allotropes, we predict a complete set of single-crystalline elastic constants, directional dependence of the single-crystalline Young modulus and homogenized polycrystalline elastic moduli.
|
|
|
Investigating ground state of nickel nitrides NiN and Ni2N with the help of quantum-mechanical calculations
Elstnerová, P. ; Friák, Martin ; Šob, Mojmír ; Neugebauer, J.
We have employed quantum mechanical calculations to identify ground-state structures of nickel nitrides NiN and Ni2N for which experimental data are lacking. In total 19 crystalline phases have been calculated for which not only thermodynamic but also structural and selected elastic properties have been determined. Employing density functional theory (DFT) methods, the total energies were calculated by means of a pseudopotential approach implemented in the VASP code and selected states were benchmarked by the full-potential linearized augmented plane wave (FP-LAPW) method implemented in the WIEN2k code. For the exchange-correlation energy the generalized gradient approximation (GGA) has been used.
|
guest ::
