Search Results (10)

Determining the concentration of light elements in the Earth’s outer core is crucial for understanding the generation of the geomagnetic field, as well as the Earth’s internal dynamics and thermal evolution. However, as a potential dominant light element in the outer core, the precise composition of silicon (Si) is still a topic of intense debate. Due to the limited experimental data, significant controversies exist between theoretical models and experimental predictions regarding the Si content in the outer core. In this work, we have calculated pressure (P)–volume (V)–temperature (T) data of Fe-X wt.% Si, where X = 0, 2.4, 4.9, 7.5, and 10.3 at ~136–330 GPa and 4000–7000 K by first-principles molecular dynamics (FP-MD) simulations. We employed pressure correction to address the discrepancy between theoretical and experimental measurements. Based on the corrected data, we established an equation of state (EoS) for Fe-Si alloys. We calculated thermodynamic properties, including density (ρ), thermal expansivity, Grüneisen parameter, isothermal and adiabatic bulk moduli, and sound velocity (V_P). To constrain the silicon content in the outer core, the ρ and V_P of Fe-X wt.% Si computed along the outer core geotherm were compared with the Preliminary Reference Earth Model (PREM). Assuming Si is the only light element in the outer core and is constrained by PREM data, the maximum Si content at T_ICB = 5400 K is 2.4 ± 1.7 wt.%. Considering the uncertainty in T_ICB, the maximum Si content in the outer core ranges from 1.8 to 3.0 ± 1.7 wt.%. The fact that a homogeneous binary alloy cannot match all seismic observations provides evidence that the content of Si in the outer core may vary with depth. Besides, the work states that pressure correction helps bridge the gap between theoretical and experimental estimates of Si concentration. The pressure-corrected equation of state provides a robust benchmark for constraining multi-component core models. Full article

In this study, first-principles molecular dynamics (FPMD) simulations were employed to systematically investigate the effects of temperature and composition on the microstructure and transport properties of CaCl₂–CaI₂ mixed molten salts at the atomic scale. Structural analysis shows that the system exhibits good relaxation behavior and thermodynamic stability, with coordination strength following Ca-Cl > Ca-I. The transport properties reveal a coupled dependence on temperature and composition: increasing CaI₂ content enhances the diffusion of I⁻ ions, whereas at 1173 K, a decrease in diffusion coefficients is observed for all ionic species. Arrhenius analysis indicates that increasing CaI₂ content lowers the activation energy for ion migration. The shear viscosity follows the order η(Ca²⁺) > η(Cl⁻) ≥ η(I⁻), and decreases with increasing temperature and CaI₂ concentration, indicating improved fluidity. Notably, the results reveal a competitive coordination mechanism between Cl⁻ and I⁻ around Ca²⁺, as well as a non-monotonic transport behavior at high temperatures, reflecting the complex coupling between composition and ionic dynamics in mixed halide melts. This study provides a theoretical basis for the optimization of molten salt electrolysis processes and nuclear energy materials, and offers insight for future multiscale simulations and experimental validation. Full article

Chlorine (Cl) and sulfur (S) are two crucial mineralizing agents in silicate melts, and are closely related to the genesis of metallic mineral deposits. Magmatic ore deposits usually form in mafic–ultramafic silicate melts by the separation (liquation) of a cooling, sulfur-rich magma into two immiscible liquids. It is not easy to identify the complexation between gold (Au), cooper (Cu) and Cl, S using the current experiment methods, and the coordination of Au and Cu with Cl and S is still unclear in mafic–ultramafic silicate melts. In this study, by using first-principles molecular dynamics technique, we investigated the structure of Au, Cu, Cl and S in the (a) anhydrous and (b) hydrous peridotite melt to reveal their coordination geochemistry. Our results show that Si⁴⁺–Cl⁻, Cu⁺–O²⁻, Au⁺–O²⁻, Cu⁺–Cl⁻, Au⁺–Cl⁻, Au⁺–S²⁻, and Cu⁺–S²⁻ cannot form stable ion pairs in silicate melts; therefore, Au⁺ and Cu⁺ cannot form stable complexes with S²⁻, O²⁻ or Cl⁻ in the melts. But the diffusion coefficients of Au⁺, Cu⁺, S²⁻ and Cl⁻, their RDF values and the bonding time ratio of the silicate melt systems show that, although they cannot form stable complexes, within the range of effective chemical bond lengths, they have a high probability of approaching and interacting with each other, which enables them to form crystal embryos or liquid-phase molecules during magma evolution. Full article

The pyrometallurgical reprocessing of spent fuel developed by the United States is currently one of the most promising nuclear fuel reprocessing methods. The electroreduction, electrolytic refining, and electrodeposition processes involve electrochemical research in high-temperature molten chloride systems. In recent years, much progress has been made in simulating and studying molten-salt systems from a microscopic perspective using the first-principles molecular dynamics (FPMD) simulation technique. Using this method for simulation calculations is more conducive to analyzing the microscopic action mechanism and microscopic mechanism in the system from the atomic level and explaining the internal reasons for various electrochemical behaviors and phenomena. This opens up a new path for the study of molten-salt electrochemical systems. However, there are still a few systematic reviews of simulating work in first-principles computation. Therefore, this work summarizes the theoretical calculation work on molten-salt electrochemical systems of recent years, focusing on the research progress in computational aspects such as coordination properties, physical properties, and electrode behavior, which has good guiding value for the application of FPMD in molten-salt electrochemistry. Full article

We performed first-principle molecular dynamics (FPMD) calculations to test the total attraction force on a physisorbed molecule at a given temperature and ambient pressure and applied it to the hydrogen storage on the 2D material MoP2. We considered a pristine material and one with 12.5% of Mo vacancies. By optimization, we calculated a gravimetric capacity for pristine MoP2 of 5.72%, with an adsorption energy of −0.13 eV/molecule. We found 6.02% and −0.14 eV/molecule for the defective surface. Next, we applied our approach to determine if the molecular hydrogen physisorption obtained by simple energy optimization exists for a given temperature and ambient pressure. We used this approach to determine the number of molecules adsorbed on the surface at a given temperature. Thus, we conducted a FPMD calculation at temperature T₁, using optimization as the initial system configuration. Subsequently, we performed a second FPMD calculation at a temperature T₂ (with T₂ << T₁), using the steady configuration of the first FPMD calculation as the initial configuration. We identified as adsorbed molecules at temperature T_1, only those forced back toward the surface at temperature T₂ due to kinetic energy loss at the lower temperature. The defective surface gave the best gravimetric capacity, ranging from 5.27% at 300 K to 6.02% at 77 K. The latter met the requirement from the US-DOE, indicating the potential practical application of our research in hydrogen storage. Full article

First-principles molecular dynamics (FPMD) calculations were performed on liquid GeSe₄ with the aim of inferring the impact of dispersion (van der Waals, vdW) forces on the structural properties. Different expressions for the dispersion forces were employed, allowing us to draw conclusions on their performances in a comparative fashion. These results supersede previous FPMD calculations obtained in smaller systems and shorter time trajectories by providing data of unprecedented accuracy. We obtained a substantial agreement with experiments for the structure factor regardless of the vdW scheme employed. This objective was achieved by using (in addition to FPMD with no dispersion forces) a selection of vdW schemes available within density functional theory. The first two are due to Grimme, D2 and D3, and the third one is devised within the so-called maximally localized Wannier functions approach (MLWF). D3 results feature a sizeable disagreement in real space with D2 and MLWF in terms of the partial and total pair correlation functions as well as the coordination numbers. More strikingly, total and partial structure factors calculated with D3 exhibit an unexpected sharp increase at low k. This peculiarity goes along with large void regions within the network, standing for a phase separation of indecipherable physical meaning. In view of these findings, further evidence of unconventional structural properties found by employing D3 is presented by relying on results obtained for a complex ionic liquid supported on a solid surface. The novelty of our study is multifold: new, reliable FPMD data for a prototypical disordered network system, convincing agreement with experimental data and assessment of the impact of dispersion forces, with emphasis on the intriguing behavior of one specific recipe and the discovery of common structural features shared by drastically dissimilar physical systems when the D3 vdW scheme is employed. Full article

As an important inorganic material, zirconium dioxide (ZrO₂) has a wide range of applications in the fields of microelectronics, coating, catalysis and energy. Due to its high dielectric constant and thermodynamic stability, ZrO₂ can be used as dielectric material to replace traditional silicon dioxide. Currently, ZrO₂ dielectric films can be prepared by atomic layer deposition (ALD) using water and zirconium precursors, namely H₂O-based ALD. Through density functional theory (DFT) calculations and first-principles molecular dynamics (FPMD) simulations, the adsorption and dissociation of water molecule on the ZrO₂ surface and the water–solid interface reaction were investigated. The results showed that the ZrO₂ (111) surface has four Lewis acid active sites with different coordination environments for the adsorption and dissociation of water. The Zr atom on the surface can interacted with the O atom of the water molecule via the p orbital of the O atom and the d orbital of the Zr atom. The water molecules could be dissociated via the water–solid interface reaction of the first or second layer of water molecules with the ZrO₂ (111) surface. These insights into the adsorption and dissociation of water and the water–solid interface reaction on the ZrO₂ surface could also provide a reference for the water–solid interface behavior of metal oxides, such as H₂O-based ALD. Full article

Using structural relaxation calculations and first-principles molecular dynamics (FPMD), we performed numerical simulations to explore the interaction of a 2D MoS₂ surface and a platinum atom, calculating the optical properties of the resulting material. We explored three initial positions for the interaction of the Pt atom and the pristine MoS₂ surface, plus another position between Pt and the MoS₂ surface with a sulfur vacancy V_S. The surface absorbed the Pt atom in all cases considered, with absorption energies ranging from −2.77 eV to −5.83 eV. We calculated the optical properties and band structure of the two cases with the largest absorption energies (−3.45 eV and −5.83 eV). The pristine MoS₂ is a semiconductor with a gap of around 1.80 eV. With the adsorption of the Pt atom (the −3.45 eV case), the material reduces its band gap to 0.95 eV. Additionally, the optical absorption in the visible range is greatly increased. The energy band structure of the 2D MoS₂ with a sulfur vacancy V_S shows a band gap of 0.74 eV, with consequent changes in its optical properties. After the adsorption of Pt atoms in the V_S vacancy, the material has a band gap of 1.06 eV. In this case, the optical absorption in the visible range increases by about eight times. The reflectivity in the infrared range gets roughly doubled for both situations of the Pt-absorbed atom considered. Finally, we performed two FPMD runs at 300 K to test the stability of the cases with the lowest and highest absorption energies observed, confirming the qualitative results obtained with the structural relaxations. Full article

Using first-principles molecular dynamics (FPMD) simulations at atmospheric pressure and 300 K, we investigated the adsorption of the molecules CO and CO₂ on each of the surfaces of the 2D materials MoP₂ and NbP₂. We found that both surfaces adsorbed the carbon monoxide molecule but not the carbon dioxide. The adsorption energy on the MoP₂ surface was −0.9398 eV, and on the NbP₂ surface, −0.9017 eV. Furthermore, we obtained substantial changes in the optical properties of each 2D material after the CO adsorption. For the two materials, the optical absorption shows significant changes in the ultraviolet region. Furthermore, the two surfaces present essential changes in the ultraviolet range in the case of reflectivity. Full article

We investigated the effect of doping a hexagonal boron nitride surface (hBN) with Ti or Pt on the adsorption of CO₂. We performed first-principles molecular dynamics simulations (FPMD) at atmospheric pressure, and 300 K. Pristine hBN shows no interaction with the CO₂ molecule. We allowed the Ti and Pt atoms to interact separately, with either a B-vacancy or an N-vacancy. Both Ti and Pt ended chemisorbed on the surface. The system hBN + Ti always chemisorbed the CO₂ molecule. This chemisorption happens in two possible ways. One is without dissociation, and in the other, the molecule breaks in CO and O. However, in the case of the Pt atom as dopant, the resulting system repels the CO₂ molecule. Full article