Ab initio study of the structural, mechanical, and dynamical properties of the rare-earth dihydrides XH2 (X=Sc, Y, and La)

Jin, Yang; Gao, Tao; Guo, Lin

doi:10.1016/j.physb.2013.08.008

Cited by 28 publications

(14 citation statements)

References 33 publications

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“…Finally, we investigated the thermodynamic properties of α‐U. Table lists the calculated temperature variations of the entropy values S , the enthalpy difference H − H 298.15 (kJ mol −1 ), and the Gibbs energy difference G − G 298.15 (kJ mol −1 ) of α‐U from 298.15 to 941 K under 0, 20, 40, 60, 80, and 100 GPa using the QHA , comparison with previous thermodynamic experimental data . QHA approximation is very valid for a large class of materials including Th metal .…”

Section: Resultsmentioning

confidence: 99%

“…The heat capacity for α‐U increases very rapidly with T 3 and it is strongly dependent on the temperature, this can be ascribed to the anharmonic effect of the phonon at sufficiently low temperatures, the higher the pressure, the smaller the heat capacity. However, C v follows the Debye model and almost approaches the Dulong–Petit limit when the temperature is higher than about 600 K. In order to obtain the more ideal value of the thermodynamic functions, the effects of higher‐order anharmonicity interaction of α‐U need to be considered, which will be the future work.…”

Section: Resultsmentioning

confidence: 99%

“…Figure 11 The Raman-active modes at G-point under high pressure. (kJ mol À1 ) of a-U from 298.15 to 941 K under 0, 20, 40, 60, 80, and 100 GPa using the QHA [33], comparison with previous thermodynamic experimental data [44]. QHA approximation is very valid for a large class of materials including Th metal [45].…”

Section: Lattice Dynamical Propertiesmentioning

confidence: 91%

“…The phonon properties are calculated using 2 × 2 × 2 supercell with 32 atoms. As is known, thermodynamic properties of solid materials can be determined by phonon density of state calculation using the QHA . The entropy ( S ) and the heat capacity ( C v ) are obtained utilizing calculated phonon density of states (PDOS) as follows, respectively :

S = r k_{normalB} \int_{0}^{\infty} g false(ω false) ({}, ((), \frac{ℏ ω}{2 k_{B} T}) ([], coth ((), \frac{ℏ ω}{2 k_{B} T}) - 1) - ln ([], 1 - exp ((), - \frac{ℏ ω}{k_{B} T}))) d ω,

C_{normalv} = r k_{normalB} {\int_{0}^{\infty} g false(ω false) ((), \frac{ℏ ω}{k_{B} T})}^{2} \frac{exp (\frac{ℏ ω}{k_{normalB} T})}{{[exp (\frac{ℏ ω}{k_{normalB} T}) - 1]}^{2}} d ω,

where r is the number of degrees of freedom in the cell, k B is the Boltzmann constants, g ( ω ) is the phonon density of states, ω is the phonon frequency, and h is the Planck constant.…”

Section: Methodsmentioning

confidence: 99%

“…The phonon properties are calculated using 2 Â 2 Â 2 supercell with 32 atoms. As is known, thermodynamic properties of solid materials can be determined by phonon density of state calculation using the QHA [33,34]. The entropy (S) and the heat capacity (C v ) are obtained utilizing calculated phonon density of states (PDOS) as follows, respectively [35]:…”

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confidence: 99%

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Ab initio investigations of electron correlation effect and phonon dynamics of orthorhombic uranium

Yang

Gao

Liu

et al. 2014

Physica Status Solidi (b)

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We have performed first principles calculations for the electronic, dynamical, and thermodynamic properties of a-U using the projector augmented wave (PAW) method. The optimized lattice parameters, equilibrium volume, atomic energy, bulk modulus, and its pressure derivative are close to the experimental data and other calculations. To evaluate the strong on-site Coulomb repulsion among the localized uranium 5f electrons, the generalized gradient approximation (GGA)þU formalism have been adopted. It is shown that the total DOS at the Fermi energy level mainly comes from the contribution of narrow f band, the electron correlation effect is small for metallic bands of uranium. In particular, the phonon spectrum of a-U is calculated within density functional perturbation theory (DFPT) as well as the small displacement method, the coincidence between our calculations and Crummett et al.'s inelastic neutron scattering measurements indicates that both phonon methods based on PAW scheme are reasonable to capture the anomalous phonon properties of a-U. The calculated dynamical properties of uranium under pressure suggest that Cmcm uranium should be stabilized dynamically at least up to 100 GPa, which accords with X-ray diffraction experimental results of Le Bihan et al. The thermodynamic functions of a-U under high temperature and high pressure are also obtained further.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Lattice Dynamical Propertiesmentioning

confidence: 91%

S = r k_{normalB} \int_{0}^{\infty} g false(ω false) ({}, ((), \frac{ℏ ω}{2 k_{B} T}) ([], coth ((), \frac{ℏ ω}{2 k_{B} T}) - 1) - ln ([], 1 - exp ((), - \frac{ℏ ω}{k_{B} T}))) d ω,

C_{normalv} = r k_{normalB} {\int_{0}^{\infty} g false(ω false) ((), \frac{ℏ ω}{k_{B} T})}^{2} \frac{exp (\frac{ℏ ω}{k_{normalB} T})}{{[exp (\frac{ℏ ω}{k_{normalB} T}) - 1]}^{2}} d ω,

where r is the number of degrees of freedom in the cell, k B is the Boltzmann constants, g ( ω ) is the phonon density of states, ω is the phonon frequency, and h is the Planck constant.…”