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Cao Q.-L.,Yibin University | Duo-Hui H.,Yibin University | Qiang L.,Yibin University | Wang F.-H.,Yibin University | And 3 more authors.
Physica B: Condensed Matter | Year: 2012

Molecular dynamics simulations of the melting curve of tantalum for the pressure range 0-300 GPa are reported. The calculated melting curve agrees well with shock wave measurements and other calculations, but disagrees strongly with the diamond anvil cell data at high pressure. Calculated results for the pressure dependence of the fusion volume and entropy show that the pressure dependence of melting temperature approximately followed the Clausius-Clapeyron relation, and the slope of melting curve is mainly due to the variation of fusion volume. Entropy change due to latent volume change in melting, Δ SV and change in the configuration, Δ SD were evaluated. It is found that they have similar trend as the overall entropy change in melting, and Δ SD is more dominant. Furthermore, the value of Δ SD at ambient pressure is close to Rln2 per mole, which is the specific value of Δ SD predicted by the Rln2 rule, while it decreases when pressure goes from 50 to 300 GPa. The analysis of the pair distribution function at extreme pressure shows that the change of configuration on melting decreases with increasing pressure, which supports the pressure dependence of Δ SD. © 2012 Elsevier B.V. All rights reserved.

Cao Q.-L.,Yibin University | Wang P.-P.,Yibin University | Huang D.-H.,Yibin University | Li Q.,Yibin University | And 2 more authors.
Journal of Chemical and Engineering Data | Year: 2013

Molecular dynamics simulations of the melting curves of six metals including Ag, Cu, Al, Mg, Ta, and Mo for the pressure range (0 to 15) GPa are reported. The melting curves of Ag, Cu, Al, and Mg fully confirm measurements and previous calculations. Meanwhile, the melting curves of Ta and Mo are consistent with previous calculations but diverge from laser-heated diamond-anvil cells values at high pressure. Our results suggest that the melting slope at 100 kPa is related to the electronic configuration of the element. In addition, the pressure dependence of fusion entropy and fusion volume are calculated up to 15 GPa. The overall fusion entropy is separated into topological entropy of fusion (ΔSD) due to the configuration change in melting and the volume entropy of fusion (ΔSV) due to the latent volume change in melting. Furthermore, we checked the R ln 2 rule under high pressure, according to which the value of ΔSD is a constant at ambient pressure. Result shows that the value of ΔS D is close to R ln 2 at ambient pressure and reflects a slow decrease when pressure increases. © 2012 American Chemical Society.

Li Q.,Yibin University | Huang D.-H.,Yibin University | Cao Q.-L.,Yibin University | Wang F.-H.,Yibin University | And 3 more authors.
Chinese Physics B | Year: 2012

Within the framework of the quasiharmonic approximation, the thermodynamics and elastic properties of Ta, including phonon density of states (DOS), equation of state, linear thermal expansion coefficient, entropy, enthalpy, heat capacity, elastic constants, bulk modulus, shear modulus, Young's modulus, microhardness, and sound velocity, are studied using the first-principles projector-augmented wave method. The vibrational contribution to Helmholtz free energy is evaluated from the first-principles phonon DOS and the Debye model. The thermal electronic contribution to Helmholtz free energy is estimated from the integration over the electronic DOS. By comparing the experimental results with the calculation results from the first-principles and the Debye model, it is found that the thermodynamic properties of Ta are depicted well by the first-principles. The elastic properties of Ta from the first-principles are consistent with the available experimental data. © 2012 Chinese Physical Society and IOP Publishing Ltd.

Sun Y.-Y.,Southwest Jiaotong University | Liu F.-S.,Southwest Jiaotong University | Xu L.-H.,Southwest Jiaotong University | Liu Q.-J.,Southwest Jiaotong University | And 2 more authors.
Molecular Physics | Year: 2015

Local hydrogen-bonding environments have important influences on the intra-molecular O-H stretchings of H2O molecules. The relationship between the contributions of intra-molecular O-H stretching and the local hydrogen-bonding environments is investigated using ab initio simulation for a condensed H2O system at 300 K, 1.7 g/cm3, and calculated/estimated pressure of approximately 9 GPa. The calculation results demonstrate that the local hydrogen-bonding environments around the two intra-molecular hydrogen atoms are not always similar. The existence of asymmetric local hydrogen environments will result in decoupling of the intra-molecular O-H stretchings in the molecule; thus, the broad O-H stretching band may be decomposed into a sum that includes isolated intra-molecular O-H stretchings but not symmetric stretching and asymmetric stretching. This research serves as a reminder to pay attention to the influence of an asymmetric local hydrogen-bonding environment on the vibrational details of the H2O molecular system and will facilitate the interpretation of measurements of the infrared and Raman spectra of the condensed H2O systems. © 2014 © 2014 Taylor & Francis.

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