Ab Initio Molecular Dynamics Simulations Research Articles

Active species in chloroaluminate ionic liquids catalyzing low-temperature polyolefin deconstruction

Chloroaluminate ionic liquids selectively transform (waste) polyolefins into gasoline-range alkanes through tandem cracking-alkylation at temperatures below 100 °C. Further improvement of this process necessitates a deep understanding of the nature of the catalytically active species and the correlated performance in the catalyzing critical reactions for the tandem polyolefin deconstruction with isoalkanes at low temperatures. Here, we address this requirement by determining the nuclearity of the chloroaluminate ions and their interactions with reaction intermediates, combining in situ 27Al magic-angle spinning nuclear magnetic resonance spectroscopy, in situ Raman spectroscopy, Al K-edge X-ray absorption near edge structure spectroscopy, and catalytic activity measurement. Cracking and alkylation are facilitated by carbenium ions initiated by AlCl3-tert-butyl chloride (TBC) adducts, which are formed by the dissociation of Al2Cl7− in the presence of TBC. The carbenium ions activate the alkane polymer strands and advance the alkylation cycle through multiple hydride transfer reactions. In situ 1H NMR and operando infrared spectroscopy demonstrate that the cracking and alkylation processes occur synchronously; alkenes formed during cracking are rapidly incorporated into the carbenium ion-mediated alkylation cycle. The conclusions are further supported by ab initio molecular dynamics simulations coupled with an enhanced sampling method, and model experiments using n-hexadecane as a feed.

Phase transitions limit lithium adsorption in titanium-based ion sieves

Hydrogen titanium oxide (HTO) is a promising material in extracting lithium ions from dilute sources such as geothermal or oil/gas brines. However, experiments show limited Li adsorption in HTO compared to its theoretical maximum capacity, where all H atoms in HTO are replaced by Li that forms lithium titanium oxide (LTO). Here, ab initio molecular dynamics (AIMD) simulations show clear evidence of phase transitions at specific Li adsorption in pure or doped HTO/LTO, which directly predict their experimental maximum capacity. Analysis of thermodynamic properties as well as layered crystal structures show distinct Li-poor to Li-rich phase transitions in the pure, Mo-doped, and Fe-doped HTO/LTO. In addition, it is observed a second phase transition in the Fe-doped HTO/LTO in the Li-poor phases that further constrains Li adsorption. To the best of my knowledge, this is the first study that accurately predict the experimental capacities in ion sieves from first principle. More importantly, this study puts spotlights on phase transitions as an important consideration in molecular engineering developments of functional separation materials, such as the high-performance lithium-ion sieves presented herein.

Effect of nitrogen-containing groups on the reduction of copper ions: In situ Raman and AIMD

In situ Raman spectroscopy and ab initio molecular dynamics (AIMD) were utilized to observe and analyze the micro-scale variations of levelers on the cathode surface. The cathodic polarization and charge transfer resistance of the three electroplating systems were examined using electrochemical methods. The throwing power of the printed circuit board coating and the nucleation changes at various times were investigated using an OLYMPUS confocal laser microscope and a scanning electron microscope. Based on the first-principles and AIMD calculations, the energy gaps, adsorption energies, and dynamic changes over 20 ps for the three levelers were determined, and the molecular mechanisms of action on the copper surface were analyzed to demonstrate alterations in the coating thickness. Experimental and theoretical results indicate that 2-thiazole-2-thiol possesses the strongest inhibitory energy, significantly repelling copper ions from migrating to the far end. On the surface, 4,6-dimethyl-2-pyrimidinethiol decomposes to form nitrogenous and sulfurous groups, which inhibit and adsorb copper ions. The adsorption states of the three levelers were thoroughly validated using Raman spectroscopy, corroborating the AIMD simulation results.

Local bandgap narrowing in the forming state of threshold switching materials

Threshold switching (TS) materials, such as amorphous chalcogenide, have received significant attention for their application in storage class memory and in-memory computing. These materials contribute to efficient data processing and reduced power consumption in data centers. The initial switching process after fabricating a TS device, known as “forming,” has a profound impact on its subsequent TS behavior. However, it remains unclear how TS materials undergo changes in their atomic and electronic structures during the forming process. Consequently, the key factors that govern TS behavior remain obscure, necessitating a deeper understanding of the underlying physics behind TS phenomena. In this Letter, we investigated the forming state of the TS material AlTeN by combining scanning internal photoemission microscopy (SIPM) and ab initio calculations. Thanks to nondestructive evaluation by SIPM measurements, we observed local bandgap narrowing of AlTeN after its forming process. This is an experimental demonstration showing the presence of nuclei of the conductive filament formed in its ON state. Moreover, we conducted an ab initio calculation to reveal the origin of bandgap narrowing. We applied strong electrothermal stresses to the AlTeN model by ab initio molecular dynamics simulation with high electronic and lattice temperatures. By quenching from the electrothermal stress conditions, we reproduced an experimentally observed forming state with a narrowed bandgap. Analysis of the electronic structures of the forming state revealed that the origin of bandgap narrowing is the generation of the valence band top and conduction band bottom stemming from the increased homopolar bonds.

Exploring the Structural and Electronic Properties of Niobium Carbide Clusters: A Density Functional Theory Study.

This paper systematically investigates the structure, stability, and electronic properties of niobium carbide clusters, NbmCn (m = 5, 6; n = 1-7), using density functional theory. Nb5C2 and Nb5C6 possess higher dissociation energies and second-order difference energies, indicating that they have higher thermodynamic stability. Moreover, ab initio molecular dynamics (AIMD) simulations are used to demonstrate the thermal stability of these structures. The analysis of the density of states indicates that the molecular orbitals of NbmCn (m = 5, 6; n = 1-7) are primarily contributed by niobium atoms, with carbon atoms having a smaller contribution. The composition of the frontier molecular orbitals reveals that niobium atoms contribute approximately 73.1% to 99.8% to NbmCn clusters, while carbon atoms contribute about 0.2% to 26.9%.

Coordination structures and stabilities of Am(III) adsorption complexes at kaolinite(0 0 1)-water interface

Understanding the structures and stabilities of actinide species is crucial for comprehending the sorption mechanisms at mineral–water interfaces. However, the relevant molecular-level fundamental aspects of actinide coordination chemistry at the mineral–water interface remain unclear. We herein conduct a systematic theoretical study of coordination structures and adsorption energies of Am3+ and Am(OH)2+ sorption complexes at the kaolinite(001)-water interface by integrating static density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. Computational results show that stable outer- and inner-sphere adsorption complexes are respectively formed through hydrogen bonding and coordinate bonding with surface aluminol groups. The most stable inner-sphere species are predicted to be tridentate surface complexes with an eight-folded coordination structure in the first coordination sphere of Am(III). This work deepens the understanding of Am(III) adsorption and complexation behaviors at the mineral–water interface, providing essential insights for actinide migration in natural environments and nuclear waste disposal. The synergy between static DFT calculations for initial screening and AIMD simulations for comprehensive dynamic analysis in this work enhances the efficiency and accuracy of theoretical predictions for actinide environmental chemistry and can be helpful for the broader research fields of geochemistry and environmental science.

Tin doping modulates electron-hole recombination in Dion-Jacobson phase 2D hybrid perovskite

To obtain less-toxic and optimal-band-gap perovskite materials, tin (Sn)-lead (Pb) hybrid technology comes into the sight of researchers. The Sn–Pb ratio primarily affects the electronic band structure, conductivity, and carrier transport, which are essential for optoelectronic performance. While most reports are about 3D materials, there has been little coverage of 2D Sn–Pb perovskites which exhibiting improved stability. In this paper, the e-h recombination dynamics in Dion-Jacobson Phase 2D Sn–Pb perovskites are studied using time-dependent ab initio nonadiabatic molecular dynamics (NAMD) simulation. It is found that Sn doping plays a significant role in narrowing the band-gap of 2D perovskites and localizing the charge distribution. Only a small amount of Sn doping can minimize NA coupling and shorten decoherence time of frontier orbitals simultaneously, then leading to longer charge recombination time. NAMD simulations reveal the optimal Sn ratio (25 mol%) and provide an effective way to design high-performance 2D perovskite materials.

Iron isotope fractionation between metal and silicate during core-mantle differentiation in rocky bodies

Fe isotope variations in rocky bodies reveal fundamental information about planetary evolution. However, experimental results have come to contradictory conclusions on the equilibrium Fe isotope fractionation between metal and silicate during core-mantle differentiation. Many different processes, including evaporation, core formation, partial melting and disproportion of mantle silicate, have been consequently proposed to explain the observed Fe isotope variations in rocky solar system bodies. Here we perform ab initio molecular dynamics simulations and find that the anharmonicity in iron strongly decreases the force constant of Fe at low pressures (<∼50 GPa), which even reverses the equilibrium Fe isotope fractionation between metal and silicate. We conclude that pyrolitic melt is always enriched in heavy Fe isotopes relative to liquid Fe-alloys, no matter what pressure. Therefore core-mantle differentiation will play a significant role in explaining the heavy Fe isotope compositions of the mantles of some rocky bodies (e.g., Earth, the ureilite parent body, and possibly the asteroid Vesta). As all previously proposed processes for Fe isotope fractionation can only enrich the mantle-derived rocks in heavy Fe isotopes, the near/sub-chondritic Fe isotope signatures of Mars and the aubrite parent body thus imply that iron sulfide enriched in light Fe isotopes may significantly contribute to the iron components of those meteoritic samples.

A first-principles prediction of novel Janus ZrGeZ3H (Z = N, P, and As) monolayers: Raman active modes, piezoelectric responses, electronic properties, and carrier mobility.

In this article, an attempt is made to explore new materials for applications in piezoelectric and electronic devices. Based on density functional theory calculation, we construct three Janus ZrGeZ3H (Z = N, P, and As) monolayers and study their stability, piezoelectricity, Raman response, and carrier mobility. The results from phonon dispersion spectra, ab initio molecular dynamics simulation, and elastic coefficients confirm the structural, thermal, and mechanical stability of these proposed structures. The ZrGeZ3H monolayers are indirect band gap semiconductors with favourable band gap energy of 1.15 and 1.00 eV for the ZrGeP3H and ZrGeAs3H, respectively, from Heyd-Scuseria-Ernzerhof functional method. It is found that the Janus ZrGeZ3H monolayers possess both in-plane and out-of-plane piezoelectric coefficients, revealing that they are potential piezoelectric candidates. In addition, the carrier mobilities of electrons and holes along transport directions are anisotropic. Notably, the ZrGeP3H and ZrGeAs3H monolayers have high electron mobility of 3639.20 and 3408.37 cm2 V-1 s-1, respectively. Our findings suggest the potential application of the Janus ZrGeZ3H monolayers in the piezoelectric and electronic fields.

AlC3 monolayer: Highly responsive and selective gas sensing material for SF6 decomposed gases (SOF2, SO2F2 and SO2)

Sulfur hexafluoride (SF6) is widely employed in industrial applications due to its interesting insulating properties. However, under electrical discharge conditions, it can undergo decomposition, yielding hazardous gases such as SOF2, SO2F2, and SO2, which can pose significant risks due to their increased toxicity and corrosive nature, affecting human health, the environment, and equipments. In this investigation, we employed density functional theory and ab-initio molecular dynamics to evaluate the stability of AlC3 monolayer and investigate its sensing capabilities. The findings establish the AlC3 monolayer as a champion material for detecting SF6 decomposition gases, specifically SOF2, SO2F2, and SO2. Importantly, the AlC3 monolayer exhibited low sensitivity to humidity and other gases, including CO2, CO, HF, H2, HCN, and H2S, highlighting its exceptional selectivity. SO2F2 exhibited the substantial adsorption energy of −1.36 eV, a work function of 5.2 eV, and a −0.69e charge transfer. Similarly, SO2 and SOF2 displayed significant adsorption energy (-1.19 eV and −1.08 eV, respectively), work functions (4.55 eV and 4.81 eV), and charge transfers (-0.61e and 0.78e). The significant variation in work function upon SO2F2 adsorption indicates the AlC3 monolayer's potential selectivity for SO2F2 over SO2 and SOF2, making it a promising material for surface work function modulated transistors. Ab-initio molecular dynamics simulations confirm AlC3 monolayer stability after adsorption at 300 K, validating predicted positions by density functional theory.

Deep-Learning Interatomic Potential Connects Molecular Structural Ordering to the Macroscale Properties of Polyacrylonitrile.

Polyacrylonitrile (PAN) is an important commercial polymer, bearing atactic stereochemistry resulting from nonselective radical polymerization. As such, an accurate, fundamental understanding of governing interactions among PAN molecular units is indispensable for advancing the design principles of final products at reduced processability costs. While ab initio molecular dynamics (AIMD) simulations can provide the necessary accuracy for treating key interactions in polar polymers, such as dipole-dipole interactions and hydrogen bonding, and analyzing their influence on the molecular orientation, their implementation is limited to small molecules only. Herein, we show that the neural network interatomic potentials (NNIPs) that are trained on the small-scale AIMD data (acquired for oligomers) can be efficiently employed to examine the structures and properties at large scales (polymers). NNIP provides critical insight into intra- and interchain hydrogen-bonding and dipolar correlations and accurately predicts the amorphous bulk PAN structure validated by modeling the experimental X-ray structure factor. Furthermore, the NNIP-predicted PAN properties, such as density and elastic modulus, are in good agreement with their experimental values. Overall, the trend in the elastic modulus is found to correlate strongly with the PAN structural orientations encoded in the Hermans orientation factor. This study enables the ability to predict the structure-property relations for PAN and analogues with sustainable ab initio accuracy across scales.

Is Ortho-Terphenyl a Rigid Glass Former?

Ortho-terphenyl (OTP) has long been used as a model system to study the glass transition due to its apparent simplicity and a widespread assumption that it is a rigid molecule. Here, we employ terahertz time-domain spectroscopy and low-frequency Raman spectroscopy to investigate the rigidity of OTP by direct observation of the low-frequency vibrational dynamics. These terahertz phonons involve complex large-amplitude atomic motions where intramolecular and intermolecular displacements are often mixed. Comparison of experimental results with density functional theory and ab initio molecular dynamics simulations shows that the assumption of rigidity neglects important implications for the glass transition and must be revisited. These results highlight the significance of terahertz modes on elasticity, which will be even more critical in more complex systems such as biomolecules.

One-pot complexation of phytic acid and polyethyleneimine on cellulosic microfibers towards insulative and flame-resistant foam

Flame resistance is required for the deployment of bio-based materials, especially those forming cellular structures that endow thermal insulation. This study proposes a one-pot strategy to prepare cellular lignocellulosic composites with excellent flame resistance. Lignocellulosic microfibers were used as the substrate onto which a flame-retardant complex consisting of P-containing phytic acid (PA) and N-containing polyethyleneimine (PEI) was formed. Following the prediction of ab initio molecular dynamics simulation, PA and PEI are integrated onto MF-CTMP following a single-step complexation assembly triggered by pH effects. The PA-PEI modified MF-CTMP can be readily transformed into a composite solid foam by dewatering a wet foam followed by oven drying. At the expense of a slightly reduced thermal insulation (thermal conductivity increase from 33.6 ± 0.6 to 40.0 ± 0.6 mW/(m·K)) the presence of PA-PEI complexes significantly improved the mechanical performance of the foam and uniquely endows it with flame resistance. Compared to unmodified MF-CTMP foams, the composite foams showed significant improvement in the Young's, specific compression, and flexural moduli (increased by 13.5, 5.5, and 7.3 folds, respectively), a high oxygen index (up to 40.8 %) and self-extinguishing effects. The results suggest the suitability of the introduced lignocellulosic foam as an alternative to traditional synthetic polymer-based counterparts as well as inorganic matter for insulation, particularly relevant to the building sector.

Thermally frustrated phase transition at high pressure in B2-ordered FeV

X-ray diffraction measurements of equiatomic B2-ordered FeV were performed in a diamond-anvil cell at room temperature at several pressure points up to 80 GPa that showed the cubic phase to be stable with no indication of structural phase transitions. Density functional theory at 0 K predicts Fermi surface nesting, an electronic topological transition, and a phonon dynamical instability within the experimentally investigated pressure range. Nevertheless, the instability is absent in phonon dispersion curves extracted from ab initio molecular dynamics simulations below the critical volume at temperatures as low as 10 K, indicating that thermal atomic displacements can frustrate the phase transition by renormalizing the phonon dispersion curves. Ferrimagnetism is critical for the stability of the cubic phase at low temperature, but thermal atomic displacements are enough to support the structure at and above the Néel temperature.

Unveiling unconventional CH4–Xe compounds and their thermodynamic properties at extreme conditions

Inert gases (e.g., He and Xe) can exhibit chemical activity at high pressure, reacting with other substances to form compounds of unexpected chemical stoichiometry. This work combines first-principles calculations and crystal structure predictions to propose four unexpected stable compounds of CH4Xe3, (CH4)2Xe, (CH4)3Xe, and (CH4)3Xe2 at pressure ranges from 2 to 100 GPa. All structures are composed of isolated Xe atoms and CH4 molecules except for (CH4)3Xe2, which comprises a polymerization product, C3H8, and hydrogen molecules. Ab initio molecular dynamics simulations indicate that pressure plays a very important role in the different temperature driving state transitions of CH4–Xe compounds. At lower pressures, the compounds follow the state transition of solid–plastic–fluid phases with increasing temperature, while at higher pressures, the stronger Xe–C interaction induces the emergence of a superionic state for CH4Xe3 and (CH4)3Xe2 as temperature increases. These results not only expand the family of CH4–Xe compounds, they also contribute to models of the structures and evolution of planetary interiors.

Anomalous Interlayer Exciton Diffusion in WS2/WSe2 Moiré Heterostructure.

Stacking van der Waals crystals allows for the on-demand creation of a periodic potential landscape to tailor the transport of quasiparticle excitations. We investigate the diffusion of photoexcited electron-hole pairs, or excitons, at the interface of WS2/WSe2 van der Waals heterostructure over a wide range of temperatures. We observe the appearance of distinct interlayer excitons for parallel and antiparallel stacking and track their diffusion through spatially and temporally resolved photoluminescence spectroscopy from 30 to 250 K. While the measured exciton diffusivity decreases with temperature, it surprisingly plateaus below 90 K. Our observations cannot be explained by classical models like hopping in the moiré potential. A combination of ab initio theory and molecular dynamics simulations suggests that low-energy phonons arising from the mismatched lattices of moiré heterostructures, also known as phasons, play a key role in describing and understanding this anomalous behavior of exciton diffusion. Our observations indicate that the moiré potential landscape is dynamic down to very low temperatures and that the phason modes can enable efficient transport of energy in the form of excitons.

Electron, phonon, and superconducting properties of Mg2CuH6 under pressure

Recent theoretical prediction of Mg2IrH6 is a significant advance in achieving high-temperature superconductivity under atmospheric pressure, Mg2IrH6 is the hydride superconductor with the highest superconducting transition temperature (Tc ∼ 160 K) under ambient pressure so far. In general, Tc is usually related to the degree of hydrogen enrichment. As a representative of the hydrogen-poor structures, MgHCu3 was also predicted to have a Tc of 43 K under atmospheric pressure. In this work, we try to replace the Ir atom in Mg2IrH6 with the Cu atom to improve the superconductivity of the system. The phonon dispersion curves and the ab initio molecular dynamics (AIMD) simulation indicate that the novel ternary Mg2CuH6 hydride is dynamically and thermodynamically stable. But, regrettably, the Tc and electron-phonon coupling (EPC) parameters λ of Mg2CuH6 are calculated to be 12.5 K and 0.55 at 25 GPa, which is far inferior to the superconductivity of Mg2IrH6. Compared with Fm3¯m Mg2CuH6, Fm3¯m Mg2IrH6 produces obvious phonon softening in the G point near 30 meV, which significantly enhances the EPC and increases the Tc of the system. Moreover, Cu substitution for Ir results in a sharp decrease in the contribution of the electronic states for Mg and H to the total density of states at the Fermi level. The huge difference in predicted Tc between Mg2CuH6 and Mg2IrH6 and their causes may provide insights into the design of high-temperature atmospheric superconductors and help to understand the superconducting mechanisms of related systems.

Innovative 2D materials for efficient photocatalysis: A comparative study for WSi2N4, WGe2N4, and their janus counterpart WSiGeN4 monolayers

In pursuit of environmentally friendly and effective photocatalytic materials for water splitting, this research paper presents a thorough evaluation of WSi2N4, WGe2N4, and their Janus counterpart WSiGeN4 monolayers through the application of Density Functional Theory. The study elucidates the optical, electronic, and structural characteristics of these monolayers, thereby demonstrating their potential as highly favorable contenders for applications involving photocatalytic water splitting. By means of comprehensive optimization and analysis, it is shown that these monolayers possess advantageous characteristics, such as favorable band gaps, stable work functions, and stability over a broad pH range. These attributes are of utmost importance in ensuring the effectiveness of hydrogen evolution reaction (HER). The inclusion of Janus WSiGeN4, which possesses an intrinsic mirror asymmetry, significantly improves the photocatalytic efficacy of the material. This is achieved by meeting the demands of optimal redox reaction levels in both the conduction and valence bands. In conjunction with machine learning force fields, ab initio molecular dynamics (AIMD) simulations validate the thermal stability of these monolayers at 300 K. In addition, our analysis of the optical properties reveals substantial absorption in the visible spectrum - vital for photocatalytic applications powered by solar energy. In summary, the research highlights the potential of Janus WSiGeN4, WGe2N4, and WSi2N4 monolayers as multifunctional and effective substances for forthcoming photocatalytic water-splitting systems. This advancement indicates of a significant stride in the direction of sustainable energy solution development.

Water Confinement on Polymer Coatings Dictates Proton-Electron Transfer on Metal-Catalyzed Hydrogenation of Nitrite.

Enzymes can precisely control the speed and selectivity of chemical reactions by modifying locally the solvent-reactant interactions. To extrapolate these attributes to heterogeneous catalysts, we have employed thermoresponsive poly n-isopropylacrylamide (p-NIPAM) brushes bonded to silica spheres containing palladium. These polymers can form hydrogen bonds with water molecules at low temperatures (<32 °C) allowing the polymer to stay swollen. Detailed reaction kinetics of nitrite hydrogenation showed that p-NIPAM decreases the apparent activation barrier by a factor of 3 at low temperatures. Diffusion-ordered spectroscopy nuclear magnetic resonance and ab initio molecular dynamics simulations showed that when p-NIPAM is present, water molecules near the surface are less mobile. This confinement perturbs the water interaction with the metal, reducing the barrier for the proton-electron transfer reduction of nitrite. Notably, this enhancement vanishes at high temperature as the polymer collapses on itself exposing the Pd to unconfined water. The fully reversible nature of this process opens the door for creating homeostatic catalysts with controlled water-confinement.

Tungsten speciation in hydrothermal fluids

Understanding the speciation and thermodynamic properties of aqueous tungsten (W) complexes under various conditions is essential for predicting W transport in hydrothermal fluids relevant to ore formation and geothermal systems. Although previous experimental and geochemical modelling studies have provided insights into W solubility in hydrothermal systems, a comprehensive molecular-level understanding of W in hydrothermal fluids remains elusive.In this study, we employed ab initio molecular dynamics (MD) simulations to determine the speciation and coordination geometries of W(VI) complexes in NaCl, NaHS, and NaF-bearing brines at temperatures up to 600 °C and pressures up to 2 kbar. These theoretical calculations were complemented by synchrotron in-situ X-ray Absorption Spectroscopy measurements of W(VI) in chloride-, sulfide-, and fluoride-rich solutions under pressures of 600 bar and temperatures ranging from 25 to 429 °C. The speciation and geometrical properties obtained from ab initio MD simulations are in reasonably good agreement with the in-situ X-ray Absorption Spectroscopy data. Our study reveals that W-Cl complexes are not stable, and W is transported as tungstates (H2WO4(aq), HWO4− and WO42−)in NaCl-rich fluids. In sulfur-rich fluids under near-neutral pH and reduced conditions (sulfide predominant), S2− ions gradually replace O2− in tungstates to form thiotungstate complexes (WO4-xSx2−, where x = 1, 2, 3, 4). The MD results suggest that fluoride (F−) plays a significant role in W transport by forming WO3F− and WO3F22− complexes, or their hydrated ions. We employed thermodynamic integration to determine the formation constants of the WO3F− and WO3F22− complexes at temperatures up to 600 °C and 2 kbar, and extrapolated these properties across a broader range of temperatures and pressures. This study underscores the significance of W-F complexes in W transportation in fluoride-bearing, acidic to neutral (pH < 8) hydrothermal fluids. In contrast, W is most likely transported as thiotungstate complexes in sulfur-bearing hydrothermal fluids within a neutral to alkaline pH range (e.g., pH 5–8.5 at 300 °C) under reduced (sulfide-stable) conditions in the Earth’s crust. Existing models for W transport in hydrothermal ore fluids need to consider the influence of W-F and thiotungstate species.