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Classical molecular dynamics simulations have recently become a standard tool for the study of electrochemical systems. State-of-the-art approaches represent the electrodes as perfect conductors, modeling their responses to the charge distribution of electrolytes via the so-called fluctuating charge model. These fluctuating charges are additional degrees of freedom that, in a Born–Oppenheimer spirit, adapt instantaneously to changes in the environment to keep each electrode at a constant potential. Here, we show that this model can be treated in the framework of constrained molecular dynamics, leading to a symplectic and time-reversible algorithm for the evolution of all the degrees of freedom of the system. The computational cost and the accuracy of the new method are similar to current alternative implementations of the model. The advantage lies in the accuracy and long term stability guaranteed by the formal properties of the algorithm and in the possibility to systematically introduce additional kinematic conditions of arbitrary number and form. We illustrate the performance of the constrained dynamics approach by enforcing the electroneutrality of the electrodes in a simple capacitor consisting of two graphite electrodes separated by a slab of liquid water. [ABSTRACT FROM AUTHOR]

A multiscale modeling approach is developed to compute the phase diagram of the RbF–CsF binary system. The mixing enthalpies of the (Rb,Cs)F solid and liquid solutions are evaluated using density functional theory and classical molecular dynamics calculations, respectively. For the solid solution, 18 different configurations are studied with density functional theory and the surrounded atom model is applied in order to compute the configurational partition function. We also measure the solidus and liquidus equilibria using differential scanning calorimetry. Finally the RbF–CsF phase diagram is constructed using the calculated excess free enthalpies of the solid and liquid solutions and a very good agreement with our experimental data is found. [ABSTRACT FROM AUTHOR]

Room-temperature ionic liquids, RTILs, based on alkylimidazolium cations build up an interesting family of products and are considered as a promising solvent class for chemistry and electrochemistry. Their features are chemical and thermal stability, nonvolatility, high ionic conductivity, and a wide electrochemical potential window and a new RTIL is synthesized, the acidic 1-ethyl-3-methylimidazolium fluoride, which shows unique properties.

We probe the possible inclusion of salt (NaCl) in the ice VII lattice over the pressure range from 2 to 4 gigapascal. We combine data from neutron diffraction experiments under pressure and from computational structure searches based on density functional theory. We observe that the high density amorphous precursor (NaCl·10.2D2O) crystallises during annealing at high pressure in the vicinity of the phase boundary between pure ices VII and VIII. The structure formed is very similar to that of pure ice VII. Our simulations indicate that substituting water molecules in the ice VII lattice with Na+ and Cl− ions would lead to a significant expansion of the lattice parameter. Since this expansion was not observed in our experiments, the ice crystallised is likely to be pure D2O or contains only a small fraction of the ions from the salt solution. [ABSTRACT FROM AUTHOR]

The electrochemical CO 2 reduction reaction (eCO 2 RR) offers a pathway to produce valuable chemical fuels from CO 2 . However, its efficiency in aqueous electrolytes is hindered by the concurrent H 2 evolution reaction (HER), which takes place at similar potentials. While the influence of cations on this process has been extensively studied, the influence of anions remains largely unexplored. In this work, we study how eCO 2 RR selectivity and activity on a gold catalyst are affected by a wide range of inorganic and carboxylate anions. We utilize in situ differential electrochemical mass spectrometry (DEMS) for real-time product monitoring coupled with molecular dynamics (MD) simulations. We show that anions significantly impact eCO 2 RR kinetics and eCO 2 RR selectivity. MD simulations reveal a new descriptor─free energy of anion physisorption─where weakly adsorbing anions enable favorable CO 2 reduction kinetics, despite the negative charge carried by the electrode surface. By leveraging these fundamental insights, we identify propionate as the most promising anion, achieving nearly 100% Faradaic efficiency while showing high CO production rates that are comparable to those in bicarbonate. These insights underscore the vital role of anion selection in achieving a highly efficient eCO 2 RR in aqueous electrolytes.