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[Display omitted] • Structural and thermophysical properties of molten FNaBe-ZrF 4 were simulated by FPMD. • Strong competitive effect between Zr and Be had been identified from the RDFs and PMFs. • Short- and intermediate-range coordination structures of -cation-F-cation- were captured. • Density, viscosity, and thermal conductivity of molten FNaBe increased with the addition of ZrF 4. • ZrF 4 is preferably 8.70 mol% to maintain the comprehensive performance of molten mixture. Molten NaF-BeF 2 (FNaBe) eutectic salt containing a small amount of ZrF 4 additive has attracted extensive attention in the application of fuel salt carriers for the Gen IV nuclear reactor. Herein, the local structures of radial and angular distribution functions (RDFs and ADFs) as well as the thermophysical properties of densities, thermal conductivities, and viscosities for molten FNaBe- x ZrF 4 (x = 2.3 to 12.5 mol%) are investigated through first-principles molecular dynamics simulations. Compared with pure FNaBe, the additive hardly changes the nearest neighbor structures between cations and F anions but has a noticeable impact on the RDFs of F-F and Na-Na pairs. Besides, the interaction potential barriers between Zr-F and Be-F ionic pairs are quite similar, indicating that the ability of Zr and Be to capture F ions is equivalent. From ADFs, the quadrilateral Na-F-Na-F rings, corner-shared tetrahedral Be-F series, and corner-shared octahedral Zr-F cluster configurations are clearly identified. Overall, the density, thermal conductivity, and viscosity of molten FNaBe are prominently increased by the addition of ZrF 4. Eventually, it is predicted that the optimal additive concentration of ZrF 4 is 8.7 mol% considering the comprehensive physicochemical performance of the molten mixture. [ABSTRACT FROM AUTHOR]

• Phase transition behavior of NaCl–MgCl 2 eutectic was first revealed. • 5-fold coordination dominates the coordination structure of Mg2+ in NaCl-MgCl 2. • High temperature is conducive to the formation of 4-fold coordinated structure. • Simulated thermophysical properties of NaCl–MgCl 2 agree well with experiments. First principle molecular dynamics (FPMD) simulations in combination with experimental measurements are applied to investigate the phase transition behavior of NaCl-MgCl 2 eutectic salt from 823 to 573 K. First, the essential phase transition indexes of thermal expansion coefficient, density, melting point, and enthalpy of fusion for NaCl-MgCl 2 eutectic obtained by simulations and experiments are in good agreement with each other. Second, the micro-structural characteristics during phase transition are depicted by the temperature dependences of angular distribution function, radial distribution function and coordination number. The structural evolution of NaCl-MgCl 2 eutectic is illustrated from the rearrangement of polyhedral M g C l n 2 - n clusters, and it is founded that high and low temperature are conducive to the formation of 4-fold and 6-fold coordinated structure, respectively. Third, the ionic self-diffusion coefficients for NaCl-MgCl 2 eutectic are predicted and concluded that Mg2+ behaves like a complex than as a free ion resulting in less diffusivity. Therefore, the shear viscosities of molten NaCl-MgCl 2 as well as the corresponding pre-exponential factor and activation energy are evaluated considering the solvodynamic mean radius of all the diffusive particles. Ultimately, two figures of merit for molten NaCl-MgCl 2 are deduced to evaluate the heat-transfer and heat-loss performance by integrating multiple thermal properties including density, viscosity, specific heat capacity and thermal conductivity. Overall, these simulation results are in satisfactory agreement with available reference data, indicating that the FPMD simulations work extremely well in predicting the thermophysical and structural properties of NaCl-MgCl 2 , which also provide insights for the applications of binary chloride salts in thermal energy storage. [ABSTRACT FROM AUTHOR]

The local coordination structure, as well as its structural dynamics, of molten LiCl-KCl-PuCl3 mixture is revealed by first-principles molecular dynamics (FPMD) simulations in terms of radial distribution functions, partial structural factors, and van Hove correlation functions. The self-diffusion coefficients and ionic conductivities are evaluated from the mean square displacements of ions, and the viscosity is then estimated from the self-diffusion coefficient of Pu3+. It is concluded that the FPMD simulations give satisfactory results compared with existing literature values. Therefore, the FPMD simulations can provide basic physicochemical information if such information is unavailable in literature and microscopic insight into the mechanism of the pyroprocessing of spent nuclear fuels. [ABSTRACT FROM AUTHOR]

A calculation approach for redox potentials of metallic cations in molten salt is proposed by ensemble averages based on first principles molecular dynamics (FPMD) and is applied to the calculation of the redox potentials of a series of metallic cations M n + (=Cu + , Tl + , Au + , La 3+ , Ce 3+ , U 3+ , and Pu 3+ ) in molten LiCl-KCl eutectic versus reference electrode of Ag + |AgCl(s)|Ag(s) with satisfactory results. Special thermodynamic cycle is designed by using Ag + | AgCl ( s ) | Ag ( s ) as reference electrode and by enclosing the reduced metallic atoms in the molten salts, and thus the energies related to the chloride anions, as well as the absolute energies related metallic atoms or cations, are cancelled. In addition, self-diffusion coefficients of the cations, as well as ionic conductivities and viscosities of the molten salt mixtures are evaluated from FPMD. The significance and prospects of this approach and FPMD in the prediction of physicochemical properties of molten salt mixtures for the pyroprocessing of spent nuclear fuels are discussed. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations are applied to the study of proton transport in maleimide and its homologues, succinimide and phthalimide. The calculations reproduce correctly their structural characteristics and reveal the hydrogen bonding and proton hopping properties. Specifically, the calculations show that the potential barrier for proton transfer between two maleimide molecules is about 30.60 kcal mol −1 mediated by one or two water molecules with correction of solvation effect by water, and will decrease to about 13.22 kcal mol −1 if ethylphosphonic acid molecule is used as mediator with correction of solvation effect by phosphoric acid. In addition, the calculations also show that succinimide and phthalimide possess similar characteristics compared to maleimide. Finally, it is concluded that maleimide and its homologues are building block candidates for the design of high-temperature proton exchange membranes. [ABSTRACT FROM AUTHOR]

Electrochemical corrosion of alloy materials is one of the biggest challenges in the development of heat transfer and storage technology by molten salt. Here, the thermodynamic and kinetic properties as well as microstructural characteristics of divalent alloying elements (M = Ni, Co, Fe, Mn, Cr, and Ti) in molten MgCl 2 –NaCl (MN) eutectic are analyzed based on first principles molecular dynamics (FPMD) simulations and electrochemical experiments, aiming to reveal corrosion rules of alloy and explain corrosion phenomenon. First, special thermodynamic cycles are designed to calculate the redox potentials of M 2+| M couples in molten MN, which are corrected by the experimental potential of Ni2+|Ni reference electrode. Then, ionic/atomic self-diffusion coefficients of molten salt mixtures are evaluated from FPMD simulations, whose credibility is verified by the results from cyclic voltammetry and chronopotentiometry. Studies have shown that the oxidation reaction of Ti are both thermodynamically and kinetically favorable, while the reactions of Fe and Cr are advantageous in thermodynamics and kinetics, respectively. Furthermore, the Ni enrichment on the alloy surface is explained by the larger diffusivity of Ni2+ than Ni in molten MN, thereby the deposition order of Ni > Mn > Co is deduced. Last, the dynamic coordination numbers and cage volumes of cation-Cl clusters are captured, where the delayed shuttle of Cl− in molten FeCl 2 -MN verifies the strongest stability of [FeCl 6 ]4− octahedral structure and the short activation time of Cl− in molten CrCl 2 -MN results in the fast corrosion rate of Cr. [Display omitted] • Redox potentials of divalent metals in molten MN were studied by FPMD and experiments. • Oxidation reactions of Fe and Cr are separately thermodynamically and kinetically favorable. • Metal deposition or dissolution depends on the ratio of diffusion coefficients of M 2+ and M. • Shuttle intensity of Cl− in M -centered coordination cages determines the corrosion rate of M. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phase transition behavior of MgCl 2 -KCl is revealed from thermophysical properties. • Microstructural and kinetic characteristics are studied by FPMD and experiments. • 5- and 4-fold coordination dominate the K-Cl and Mg-Cl coordinated structures. • Pre-peak of static structural factor is primarily attributed to Mg-Mg across networks. First principle molecular dynamics (FPMD) simulations coupled with experimental measurements are used to investigate the thermophysical parameters, microstructures, and thermal transport properties of the MgCl 2 -KCl (32:68 mol%) eutectic salt. The phase transition behaviors are charactered by the thermal expansion coefficient, density, enthalpy of fusion, and specific heat capacity through FPMD simulations, and the simulated results cohesive well with those of our experiments. From the temperature dependences of radial distribution functions g (r) and coordination numbers, the mutations of peak heights of g K - Cl (r) and g Mg - Cl (r) near the melting point are related to the phase change, and the coordination structure of K-Cl is significantly changed from 6-fold to 5-fold with increasing temperature. Moreover, the prominent peaks in static structural factors are attributed to charge alternation structures of cation-Cl clusters, while pre-peaks are dominated by the Mg-Mg correlation. Based on ionic self-diffusion coefficients, the calculated thermal conductivity and shear viscosity of molten MgCl 2 -KCl are slightly lower than our experimental values. Nevertheless, the FPMD simulations provide an appropriate approach to evaluate the thermodynamic and kinetic properties of MgCl 2 -KCl eutectic, which contributes essential data for designing the heat transfer and storage system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermophysical properties and microstructures of molten NaCl-KCl-NaF are simulated by FPMD. • Excellent thermal energy storage and conductivity are explained from local structures. • FPMD with DFT-D3 dispersion correction is prominent in evaluating energy storage density. • Radial and angular distributions involving K and F are extremely susceptible to temperature. • Mean viscosity of molten NaCl-KCl-NaF from 923 to 1123 K is predicated as 1.308 cP. Ternary NaCl-KCl-NaF eutectic salt is a promising thermal storage and heat transfer medium for the application of high-temperature concentrated solar power due to the high energy density and thermal conductivity. However, the relationships between these properties and structures of NaCl-KCl-NaF eutectic cannot be well explained by experiments, and thus the first principles molecular dynamics (FPMD) simulations technique stands out. In the work, the initial models of molten NaCl-KCl-NaF are constructed based on experimental densities, the energy storage density and thermal conductivity are evaluated via FPMD simulations, and the origins of the two properties are explained from the microstructures of radial and angular distribution functions. It is concluded that the strong coordinated solvation shell of Na-F results in the high energy storage density. And the orientations of Cl-Cl-Cl bond angle are enlarged by addition of F anions, thereby enhancing the thermal diffusion coefficient. Finally, the viscosities of molten NaCl-KCl-NaF from 923 to 1323 K are predicted by FPMD based on the diffusion coefficient and solvodynamic mean radius, suggesting that some anions of KCl and NaF are exchanged with each other above 1123 K. Overall, these simulation results are helpful to understand the performance improvement of molten alkali halides, and to replenish and modify the molten salt database. [ABSTRACT FROM AUTHOR]

A purification protocol of molten MgCl 2 -NaCl-KCl (MNK) by adding active metals has been proposed to reduce the corrosion of alloy materials in the application of generation III concentrating solar power plants. In this work, the ionic transport properties and micro structural characteristics of metals (Mg, Na, and K) and molten MNK mixtures (metal -MNK) are investigated at 723 K by first principles molecular dynamics (FPMD) simulations. According to the evolution of total energy, the Mg -MNK is the most stable mixture, while the Na -MNK mixture has larger energy fluctuations resulting in a higher specific heat capacity. Studies have shown that the small amount of metal existing in the molten MNK has almost no effect on the ionic diffusion order, but total diffusion coefficients and thermal conductivities of metal -MNK mixtures are improved. Meanwhile, the intensity of diffracted light of molten MNK is weakened by metals, and the microstructures of molten MNK added with alkali metals are more susceptible than that with metallic Mg by analyzing the total and partial static structure factors. Furthermore, the intermediate range orders of metal- MNK are demonstrated, especially for Mg-Mg pairs hinting the formation of the Mg2+-void-Mg2+ structure or Mg2+-centered clusters. Overall, the FPMD results deeply elaborate the dynamic interactions of molten MNK and metallic particles, which give insights for the development of salt purification and corrosion inhibition technology. • Dynamic interactions between molten MNK and active metals were simulated by FPMD. • Time evolutions of density and total energy of molten metal -MNK mixtures were depicted. • Ionic diffusion coefficients and thermal conductivities of molten metal -MNK were evaluated. • Effects of Mg, Na, and K metals on microstructures of molten MNK were elaborated. [ABSTRACT FROM AUTHOR]

First principle molecular dynamics (FPMD) simulations are used to investigate the dynamic interaction of impurity water with molten MgCl 2 -NaCl-KCl which has emerged as one of attractive candidate salts for the generation III concentrated solar power plant. The energetic fluctuations, radial distribution functions, micro-morphologies of intermediates, vibrational characteristics, and ionic self-diffusion coefficients of hydrous MgCl 2 -NaCl-KCl (h MNK) systems at 773 K are demonstrated, respectively. It is concluded that the O2− will eventually tend to interact with Mg2+ regardless of the initial water distribution. Besides, the evolution of Mg–O interatomic distance over time is depicted, from which the shuttles of O2− in the coordination shell of Mg-centered polyhedrons are captured. Furthermore, the simulated stretching vibration spectra of Mg–O and H–O bonds are comparable with experimental results, suggesting the powerful predictivity of FPMD. Overall, the water in molten h MNK promotes the migration of K+ rather than Na+, and the ionic transport properties depend on the water content and spatial distribution. And these FPMD results are heuristic in understanding the structure-activity relationship of molten h MNK, which sheds insight for the development of salt purification technology. Unlabelled Image • Dynamic interaction of molten MgCl 2 -NaCl-KCl and impurity water was simulated by FPMD. • Micromorphologies of intermediates for hydrous MgCl 2 -NaCl-KCl were depicted. • Stretching vibration spectra of Mg–O and H–O bonds were analyzed. • Effect of water on ionic transport properties of molten MgCl 2 -NaCl-KCl was revealed. [ABSTRACT FROM AUTHOR]

The first principles molecular dynamics (FPMD) simulations are applied to the study of LiCl-KCl eutectic and UCl 3 in LiCl-KCl eutectic. The densities of the molten salt mixtures are optimized by FPMD simulations in NVT ensemble, and the local coordination structures are evaluated in terms of radial distribution functions and partial static structure factors. Both self-diffusion coefficients and ion conductivities are evaluated from the mean square displacements using Einstein relation for diffusion coefficients. It is conformed that the FPMD simulations give satisfactory structural and transport characteristics compared with experimental observations. Therefore, the predictability of FPMD simulations for structural and transport characteristics of molten salt mixtures is confirmed, and the FPMD simulations can be useful measurement in the establishment of database of actinide behavior in molten salt mixtures essential for the pyroprocessing of spent nuclear fuels. [ABSTRACT FROM AUTHOR]

[Display omitted] • A modified embedded-atom model (MEAM) is developed for cesium. • The MEAM reproduces accurately the high-pressure phase diagram for cesium. • The MEAM is better than EAM and DFT using PBE functional. • Structural and physical characteristics are evaluated based on our MEAM. • The MEAM reproduces the melting process and melting point of cesium. A modified embedded-atom model (MEAM) is developed for cesium to reproduce its high-pressure phase transition and compared with the embedded-atom model (EAM) and the PBE (Perdew-Burke-Ernzerhof) functional. The MEAM reproduces successfully the high-pressure phase transition from body-centered cubic (bcc) structure to face-centered cubic (fcc) structure at 0 K in terms of formation energy as a function of pressure, and the evaluated compression curve agrees satisfactorily with the experimental observations reported in literatures. Though the EAM can also reproduce the high-pressure phase transition, it behaves much stiffer than experimental observations and is almost uncompressible below 0.2 GPa at 0 K. On the other hand, the PBE functional cannot reproduce the high-pressure phase transition and the calculated results become unstable under high pressure. Finally, the elastic constants, Poisson's ratio, radial distribution function, lattice constant, vacancy formation energy, interstitial formation energy, and melting point are evaluated using molecular dynamics simulation based on the MEAM. [ABSTRACT FROM AUTHOR]