Water is a major component of fluids in the Earth’s mantle, where its properties are substantially different from those at ambient conditions. At the pressures and temperatures of the mantle, ...experiments on aqueous fluids are challenging, and several fundamental properties of water are poorly known; e.g., its dielectric constant has not been measured. This lack of knowledge of water dielectric properties greatly limits our ability to model water–rock interactions and, in general, our understanding of aqueous fluids below the Earth’s crust. Using ab initio molecular dynamics, we computed the dielectric constant of water under the conditions of the Earth’s upper mantle, and we predicted the solubility products of carbonate minerals. We found that MgCO ₃ (magnesite)—insoluble in water under ambient conditions—becomes at least slightly soluble at the bottom of the upper mantle, suggesting that water may transport significant quantities of oxidized carbon. Our results suggest that aqueous carbonates could leave the subducting lithosphere during dehydration reactions and could be injected into the overlying lithosphere. The Earth’s deep carbon could possibly be recycled through aqueous transport on a large scale through subduction zones.
Thermal conductivity is a crucial parameter for the thermal evolution of Earth's core. In this paper, the thermal conductivity of Fe-Ni-O fluid was calculated by ab initio simulations, and then age ...of inner core and thickness of thermal stratification were derived. The results indicate that the thermal conductivity of Fe-Ni-O fluid along the core adiabatic curve ranges from 111.68 to 182.33 W/m/K. The thermal conductivity at the core-mantle boundary increases monotonically with temperature as expected. The thermal conductivity of Fe-Ni-O fluid is lower than that of pure Fe and Fe-Ni fluids. The age of the inner core is determined to be 0.868 Ga in our fiducial model by calculating the energy budget in the core and time evolution of thermal conductivity of Fe-Ni-O fluid. The thickness of thermal stratification is 454 km when dTc/dt=100 K/Ga by calculating the temperature gradient.
•Thermal conductivity along the adiabatic curve ranges from 111.68 W/m/K to 182.33 W/m/K.•Temperature dependence on thermal conductivity is considered.•The age of the inner core is 0.868 Ga.•The thickness of thermal stratification is 454 km.
•Dynamics of liquid Si is studied by ab initio molecular dynamics in a pressure range above the melting line minimum;•A signal in transverse spectral functions from additional type of collective ...modes was observed;•The frequencies of the additional transverse modes coincide with the peak positions of spectra of velocity autocorrelations;•No sharp changes in single-particle and collective dynamics in the region of melting line minimum.
We report an ab initio simulation study of changes in structural and dynamic properties of liquid Si at 7 pressures ranging from 10.2 to 24.3 GPa along the isothermal line 1150 K, which is above the minimum of the melting line. The increase of pressure from 10.2 to 16 GPa causes strong reduction in the tetrahedral ordering of the closest neighbors. The diffusion coefficient shows a linear decay vs drop in atomic volume, that agrees with theoretical prediction for simple liquid metals, thus not showing any feature at the pressures corresponding to the different crystal phase boundaries. The Fourier-spectrum of the velocity autocorrelation function shows two-peak structure at pressures 20 of GPa and higher. These characteristic frequencies correspond well to the peak frequencies of the transverse current spectral function in the second pseudo-Brillouin zone. Two almost flat branches of short-wavelength transverse modes were observed at all the studied pressures. We discuss the pressure evolution of characteristic frequencies in the longitudinal and transverse branches of collective modes.
Water seeks its own level Solvent may dramatically affect heterogeneously catalyzed processes. In their Communication on page 3327 ff., D. Muñoz‐Santiburcio et al. use advanced ab initio simulations ...to explore the effect of water on methanol oxidation over titania‐supported gold nanoparticles. The liquid‐ and gas‐phase reaction mechanisms are distinctly different because water molecules actively participate in oxidation and alter charge‐transfer steps in the reaction.
The primary basis of renewable energy is transformation of light energy in the form of electrical energy that highly analyzed in past decade. By using Quantum espresso codethat based density ...functional theory, we have elucidated mechanical, electronic and optical properties of organic (CH3NH3)2AgMBr6 (M = Sb, Bi) halides. In order to treat exchange-correlation functional, we employed PBE generalized gradient approximations (GGA) to execute the mechanical and opto-electronic parameters. Our calculated results of Pugh's ratio and Poisson's ratio of both halides recommended the quality of ductility. In addition, calculations regarding electronic and optical properties are obtained by using GGA + U in-order-to deliberating the accurate band gap. The required indirect band gaps for opto-electronic applications are calculated as 0.1 eV/0.88 eV for (CH3NH3)2AgSb/BiCl6. Interestingly, significant absorption coefficients for both halides endorse that these are appropriate opto-electronic devices in near-visible and infra-red regions.
In this paper, we report on ab initio simulations results focused on completing a thorough energetic, structural, charge and mobility analysis of the synergistic behaviour of diverse defects, namely ...self-interstitial atoms (SIA) and light impurity atoms (LIA), i.e., He and H, that would appear in W when simultaneously irradiated with the latter. In particular, the influence of a W〈110〉/W〈112〉 grain boundary (GB) in the behaviour of coexisting defects is studied and compared with the results obtained in the bulk. Four possible scenarios are analysed concerning the occupation of the GBs with: (i) a single SIA (ii) the simultaneous presence of two different defects, that is, He-H or SIA-LIA pairs, and (iii) the three types of defects together. The most stable configuration in each of these scenarios is detailed. Results show that GBs act as trapping sites for SIAs and LIAs and that the interaction between He and H is weak in all the analysed arrangements. They also indicate that the introduction of a SIA in a GB preloaded with He and H affects each of the atoms differently, as the former tends to stay close to the extra W atom, while the latter finds more comfortable accommodations away from the other two defects. In bulk W, the qualitative behaviour of He and H is quite similar and the presence of a LIA strongly affects the preferred orientation of the SIA dumbbell. Additionally, defect mobilities along the GB have been assessed concluding that the SIAs tend to move along the interfacial grooves, so to recombine with the vacancies present there.
The density of the Earth's inner core is less than that of pure iron and the P-wave velocities and, particularly, the S-wave velocities in the inner core observed from seismology are lower than those ...generally obtained from mineral physics. On the basis of measurements of compressional sound velocities to ∼100 GPa in diamond-anvil cells, extrapolated to inner-core pressures, it has been suggested that both the inner-core density and P-wave velocity can be matched simultaneously by the properties of a hexagonal-close-packed (hcp) Fe–Si or Fe–Ni–Si alloy. In this paper we present the results of ab initio molecular dynamics simulations of hcp-Fe–Si alloys at 360 GPa and at temperatures up to melting. We find that although the inner-core density can be readily matched by an Fe–Si alloy, the same is not true for the wave velocities. At inner-core temperatures, the P-wave velocity in hcp-Fe–Si remains equal to, or slightly above, that of hcp-Fe and shows little change with silicon content. The S-wave velocity is reduced with respect to that of pure hcp-iron, except for temperatures immediately prior to melting, where the velocities are almost equal; this is a consequence of the fact that the strong temperature dependence of the shear modulus that was seen in similar simulations of hcp-Fe just prior to melting was not found in hcp-Fe–Si, and so in this temperature range the reduced S-wave velocity of pure iron closely matches that of the alloy. Our results show that for an hcp-Fe–Si alloy matching the inner-core density, both the P-wave and the S-wave velocities will be higher than those observed by seismology and we conclude, therefore, that our calculations indicate that inner core velocities cannot be explained by an hcp-Fe–Si alloy. The opposite conclusion, obtained previously from experimental data measured at lower pressures, is a consequence of: (i) the necessarily large extrapolation in pressure and temperature required to extend the experimental results to inner-core conditions and (ii) the use of a velocity–density relationship for pure hcp-iron that is now considered to be incorrect.
•Fe(1−x)Six alloy match the density of Earth's inner core for a wide range of x &T.•The pre-melting effect is not detected in Fe(1−x)Six alloy, in contrast to pure Fe.•Si does not modify wave velocities of pure Fe in Earth's inner core conditions.•Fe(1−x)Six alloy cannot simultaneously match VP, VS and ρ of Earth's inner core.
Many-body Green's function perturbation theories, such as the GW and Bethe-Salpeter formalisms, are starting to be routinely applied to study charged and neutral electronic excitations in molecular ...organic systems relevant to applications in photovoltaics, photochemistry or biology. In parallel, density functional theory and its time-dependent extensions significantly progressed along the line of range-separated hybrid functionals within the generalized Kohn-Sham formalism designed to provide correct excitation energies. We give an overview and compare these approaches with examples drawn from the study of gas phase organic systems such as fullerenes, porphyrins, bacteriochlorophylls or nucleobases molecules. The perspectives and challenges that many-body perturbation theory is facing, such as the role of self-consistency, the calculation of forces and potential energy surfaces in the excited states, or the development of embedding techniques specific to the GW and Bethe-Salpeter equation formalisms, are outlined.
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•Ab-initio Sn3O4 exfoliation energy lies in the van der Waals layered materials range.•A modern Scotch-tape exfoliation of a Sn3O4 nanobelt carried out using a Dual Beam ...Microscope.•As predicted theoretically, a few layers from Sn3O4 nanobelt could be exfoliated.•Using the same nanomanipulation, layers could not be removed from the SnO and SnO2.
Van der Waals (vdW) layered materials have been receiving a great deal of attention, especially after the scotch-tape experiment using graphite and the unique properties of graphene. Sn3O4, which also presents a layered structure, has been widely employed in a variety of technologies, but without further understanding of its bulk properties. For the first time, a modern Scotch-tape nanomanipulation experiment carried on a Dual Beam Microscope is combined with Density Functional Theory to investigate the Sn3O4 bulk properties. Theoretically, we have shown that the interaction energy between Sn3O4 layers are in the same order of graphene layers (21 meV Å−2), indicating its vdW interaction nature, whereas for SnO is slightly stronger (26 meV Å−2). Then, the Dual Beam Microscope nanomanipulation of the Sn3O4 nanobelts revealed the weak layer-layer interactions along their stacking direction (plane (010)). Comparatively, when probing SnO and SnO2 nanobelts, no exfoliation could be seen. The study of Sn3O4 electronic structure properties also presents the important role of the interfacial region to the valence and conduction band and, consequently, to the material band-gap. The outcome of this study will help improving some applications, e.g., knowing the total and local density of states can help understanding surface band bending following gases adsorption. To the best of our knowledge, this is the first study to show, combining experimental and theoretical techniques, Sn3O4 as a promising 2D material.
Ge
2
Sb
2
Te
5
(GST) is an important phase‐change material used in optical and electronic memory devices. In this work, crystal growth of GST at 600 K is investigated by ab initio molecular dynamics. ...Simulations of two different crystallization processes are performed. In the first set of simulations, the growth of crystalline nuclei generated using the metadynamics method is studied. In the second set, models containing a planar amorphous–crystalline interface are considered and the crystallization at the interface is investigated. The extracted crystal growth velocities are in the range of 1 m s
−1
in both cases and compare well with recent experimental measurements. It is also found that GST crystallizes into a disordered cubic phase in all the simulations.
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