Gérard Picard

Equilibrium reactions between molecular and ionic species in pure molten LiCl and in LiCl + MCl (M = Na, K, Rb) melts investigated by computational chemistry

In order to study the microscopic structures of molten lithium chloride and selected binary chloride melts containing lithium chloride, DFT calculations were performed with dmol software at the DNP/UHF/BLYP level to study all the possible (stable) isolated chloride complexes of alkaline metals. Results on geometry, energy, vibrational spectrum and Mulliken population are summarized. In addition, thermostatistical calculations were carried out to obtain the thermodynamic data relative to equilibrium reactions occuring in melts. It was demonstrated that the general equilibrium LiCl + 2 MCl /ag LiCl−2 + M2Cl+ predominates and the temperature and composition dependence of the percentage of LiCl−2 for a given melt (molten LiCl-NaCl, LiCl-KCl and LiCl-RbCl) was determined. This study emphasizes the role of the counter cation on the structure of molten alkali metal chlorides.

Topological Analysis of the Electron Localization Function: A Help for Understanding the Complex Structure of Cryolitic Melts

A theoretical study of the solvated , , and species which are involved in cryolitic melts was performed. Based on the density functional theory formalism, a structural and vibrational analysis of these isolated molecules was carried out, allowing determination of their relative stabilities. A further topological analysis of the electron localization function gradient field reveals this to be a powerful tool to provide insight into the bonding properties of these molecules. The dative‐polarized character of these species was characterized, and the structural effect of the calcium countercation was investigated.

Evidence of cations’ influence for structural rearrangements in cryolitic melts

DFT calculations were performed in order to acquire structural and energetic informations about aluminum (III) fluoride complexes and their stabilities as a function of the nature of center cation (sodium or calcium). These calculations enable us to explain the stabilizing zffzct of calcium regarding to the four‐ and five‐fold coordinated complexes against the cryolitic anion.

Computational Chemistry: A Way To Reach Spectroscopic and Thermodynamic Data for Exotic Compounds

In this paper, we report a general methodology to reach thermochemical properties of molecules in gas phase. We applied these calculations to related complexes of industrial interest, concerning the electrowinning of aluminum. This thermochemical prediction is a demonstration of a quantitative analysis after geometry optimizations and frequencies calculations from density functional computations (or any first-principle techniques). Since this methodology is completely generic, we can study any complexes of interest in order to study the model of the vapor. We have especially investigated the (Na3AlF6, Na2AlF5, NaAlF4, AlF3, NaF, (NaF)2, (NaAlF4)2) system. It has been found that NaAlF4 and (NaF)2 are the major species present in gas phase. Results concerning calcium are also presented, showing that CaAlF5 is in the vapor. Its partial pressure decreases when the one of CaF2 increases and the partial pressure of NaAlF4 (and all minor species containing aluminum) decreases at the same time.

A new method for the structural modelling of disordered compounds—application to molten NaCl

Abstract This paper describes a new method for limiting structural models during modelling procedures on disordered compounds. Instead of using the well known periodic boundary, the data derived from neutron diffraction experiments are modified to take into account a spherical limitation of the model. Compared to cubic periodic modelling, this method reduces the computation time and improves model reliability since it introduces no artificial anisotropy. The method has been tested in the structural modelling of molten NaCl.

Quantum Mechanics Applied to Ionic Dissociation in a (Li, K)X Binary Melt (X = F, Cl, Br, or I)

Quantum mechanics combined with thermostatistical computations allowed us to establish the binary lithium potassium halide melt dissociations. These latter can be well described taking into account the formation both of simple and complex ions LiX + 2KX ⇇ Li + + 2K + + 3X - ⇇ LiX 2 - + K 2 X + Except for the lithium iodide-potassium iodide molten mixtures, whose dissociations are satisfactorily described assuming the formation of simple ions only (reaction i), the existence of the ionic complexes LiX 2 - and K 2 X + explains qualitatively the electrical conductivity of melts whatever the melt composition and temperature.

Advantages and drawbacks of the quantum chemistry methodology in predicting the thermochemical data of lanthanide trihalide molecules

Abstract DFT calculations have been carried out on six lanthanide trihalide molecules, using Stuttgart ECPs on the lanthanides and a 6-31G * all-electrons basis set on the halogens. These calculations have been compared to previous theoretical and experimental data. Calculated bond lengths and vibrational frequencies are found to be in good agreement with previous theoretical results. The variations observed between experimental and theoretical results are discussed. Therefore, thermochemical data have been derived from such calculations. In this paper, the advantages and drawbacks of this methodology are discussed in the framework of the selected heavy elements. The different factors which influence the estimated thermochemical data have been compared. While molecular parameters seem to have a weak influence on the thermochemical functions, low frequencies (flat energy surfaces along the out-of-plane distortion) and the electronic partition function have been revealed to be the main factors for the accuracy of the predicted thermochemical data.

ELECTRON LOCALIZATION FUNCTION VIEW OF BONDING IN SELECTED ALUMINUM FLUORIDE MOLECULES

Abstract A series of calculations has been performed on the AlF 4 − and CaAlF 5 species in order to precise their equilibrium geometry as well as to get some insight onto their bonding properties. These species play an important role in electrochemical industrial processes such as the electrowinning of aluminum (i.e. the Heroult–Hall process). The calculations have been performed within the density functional approach using the B3LYP hybrid functional and the 6-311++G(3df,2p) all-electron basis sets on all the atomic centres. The optimized geometries and the calculated frequencies of AlF 4 − are found to be in agreement with those previously obtained at a lower level of calculation and with experiments. The bonding has been investigated by the topological analysis of the electron localization function gradient field. The analysis indicates that the Al–F bond presents a noticeable covalent character testified by the presence of a disynaptic basin between the Al and F cores. The basin’s populations and their fluctuations have been calculated indicating an important delocalization between the Al–F bond and the fluorines lone pairs. Moreover, the structural role of the counter cation Ca 2+ has been emphasized. A structural and topological analysis of CaAlF 5 has been carried out. This study has clearly established that the CaAlF 5 molecule can be described as purely ionic interactions between the F − , AlF 3 and Ca 2+ species.

Molecular modelling: An analytical tool with a predictive character for investigating reactivity in molten salt media.

Possibilities offered by Molecular Modelling for studying homogeneous and interfacial processes and reactions in melts are discussed. A few typical illustrative examples covering some of the main research fields of molten salt chemistry and electrochemistry are given. Quantum chemistry calculations, Molecular Dynamics and Monte Carlo methods appear to be fantastic tools for analyzing and predicting reactivity in molten salts.

Complexes responsible for ionic transport in LiCl‐KCl eutectic melt

DFT calculations using DMol software at the DNP/UHF/BLYP level were firstly performed in order to determine the more stable isolated chloro‐complexes of lithium and/or potassium cations. An Inverse Isotropic Monte Carlo technique was then used for obtaining a 3‐D model of this melt from the pair correlation functions computed by Lantelme and Turq. At last, DFT calculation derived complexes were looked for in the melt model using a lab‐made software. This procedure showed the presence of LiCl2− and K2Cl+ complexes in molten KCl eutectic. This procedure allows a better understanding of the structure of melt and suggests answers to some phenomena that occur in molten salts such as the Chemla effect.