Investigation of the surface charge behaviour of ettringite: Influence of pH, calcium, and sulphate ions.

Ettringite is an important mineral that contributes to the overall performance of cementitious materials. Knowledge of the surface charge behaviour of a solid is necessary for a mechanistic description of surface processes such as adsorption or particle-particle interactions. The objective of this study was to develop a model capable of reproducing ettringite surface charge as a function of calcium, sulphate, and pH.

Negative linear compressibility in nanoporous metal-organic frameworks rationalized by the empty channel structural mechanism.

Zinc squarate tetrahydrate (ZnCO·4HO) and titanium oxalate trioxide dihydrate (Ti(CO)O·2HO) are nanoporous metal-organic frameworks possessing empty channels in their crystal structures. The crystal structures and mechanical properties of these materials are studied using first principles solid-state methods based on Density Functional Theory. The results show that they exhibit the negative linear compressibility (NLC) and negative Poisson's ratio (NPR) phenomena.

Full crystal structure, hydrogen bonding and spectroscopic, mechanical and thermodynamic properties of mineral uranopilite.

The determination of the full crystal structure of the uranyl sulfate mineral uranopilite, (UO)(SO)O(OH)·14HO, including the positions of the hydrogen atoms within the corresponding unit cell, has not been feasible to date due to the poor quality of its X-ray diffraction pattern. In this paper, the complete crystal structure of uranopilite is established for the first time by means of first principles solid-state calculations based in density functional theory employing a large plane wave basis set and pseudopotential functions. The computed unit-cell parameters and structural data for the non-hydrogen atoms are in excellent agreement with the available experimental data.

Crystal Structure, Infrared Spectrum and Elastic Anomalies in Tuperssuatsiaite.

The full crystal structure of the phyllosilicate mineral tuperssuatsiaite, including the positions of the hydrogen atoms in its unit cell, is determined for the first time by using first-principles solid-state methods. From the optimized structure, its infrared spectrum and elastic properties are determined. The computed infrared spectrum is in excellent agreement with the experimental spectrum recorded from a natural sample from Ilímaussaq alkaline complex (Greenland, Denmark).

The magnesium uranyl tricarbonate octadecahydrate mineral, bayleyite: Periodic DFT study of its crystal structure, hydrogen bonding, mechanical properties and infrared spectrum.

Bayleyite is a highly hydrated uranyl tricarbonate mineral containing eighteen water molecules per formula unit. Due to this large water content, the correct description of its crystal structure is a great challenge for the first principles solid state methodology. In this work, the crystal structure, hydrogen bonding, mechanical properties and infrared spectrum of bayleyite, Mg[UO(CO)] · 18 HO, have been investigated by means of Periodic Density Functional Theory methods using plane wave basis sets and pseudopotentials.

Structural, mechanical, spectroscopic and thermodynamic characterization of the copper-uranyl tetrahydroxide mineral vandenbrandeite.

The full crystal structure of the copper-uranyl tetrahydroxide mineral (vandenbrandeite), including the positions of the hydrogen atoms, is established by the first time from X-ray diffraction data taken from a natural crystal sample from the Musonoi Mine, Katanga Province, Democratic Republic of Congo. The structure is verified using first-principles solid-state methods. From the optimized structure, the mechanical and dynamical stability of vandenbrandeite is studied and a rich set of mechanical properties are determined.

The layered uranyl silicate mineral uranophane-β: crystal structure, mechanical properties, Raman spectrum and comparison with the α-polymorph.

The crystal structure, elastic properties and the Raman spectrum of the layered calcium uranyl silicate pentahydrate mineral uranophane-β, Ca(UO2)2Si2O6(OH)2·5H2O, are studied by means of first-principles solid-state methods and compared with the corresponding information for the α polymorph. The availability of the energy optimized full crystal structure of uranophane-β, including the positions of the hydrogen atoms, made possible the computation of its elastic properties and the Raman spectrum by using the theoretical methodology. An extended set of relevant mechanical data is reported.

Crystal structure, hydrogen bonding, mechanical properties and Raman spectrum of the lead uranyl silicate monohydrate mineral kasolite.

The crystal structure, hydrogen bonding, mechanical properties and Raman spectrum of the lead uranyl silicate monohydrate mineral kasolite, Pb(UO)(SiO)·HO, are investigated by means of first-principles solid-state methods based on density functional theory using plane waves and pseudopotentials. The computed unit cell parameters, bond lengths and angles and X-ray powder pattern of kasolite are found to be in very good agreement with their experimental counterparts. The calculated hydrogen atom positions and associated hydrogen bond structure in the unit cell of kasolite confirmed the hydrogen bond scheme previously determined from X-ray diffraction data.

Thermodynamic, Raman Spectroscopic, and UV-Visible Optical Characterization of the Deltic, Squaric, and Croconic Cyclic Oxocarbon Acids.

A precise and complete thermodynamic, Raman spectroscopic, and ultraviolet-visible (UV-vis) optical characterization of the deltic, squaric, and croconic cyclic oxocarbon acids is obtained using theoretical solid-state methods employing very demanding calculation parameters. The computed fundamental thermodynamic properties include the isobaric specific heat, the entropy, the enthalpy, and the Gibbs free energy as a function of temperature. The calculated specific heats at 298.

Negative linear compressibility in uranyl squarate monohydrate.

The mechanical properties of the uranyl squarate monohydrate material, [Formula: see text], were studied using theoretical solid-state methods based in density functional theory employing plane waves and pseudopotentials. Very demanding calculation parameters were utilized in order to obtain a realistic description of the mechanical behavior of this material. Since the determination of the positions of the hydrogen atoms in the unit cell of uranyl squarate monohydrate was not possible from x-ray diffraction data by structure refinement, they were fully optimized theoretically.

Mechanical properties of anhydrous oxalic acid and oxalic acid dihydrate.

The mechanical properties of oxalic acid dihydrate and anhydrous oxalic acid (α and β polymorphic forms) were obtained by using rigorous theoretical solid-state methods based on density functional theory using plane waves and pseudopotentials. The calculated crystal structures and X-ray powder diffraction patterns of these materials were found to be in excellent agreement with the experimental information. Since the calculated elasticity matrices fullfilled the Born stability conditions, the corresponding crystal structures were found to be mechanically stable.

Becquerelite mineral phase: crystal structure and thermodynamic and mechanical stability by using periodic DFT.

The structure, thermodynamic and mechanical properties of becquerelite mineral, Ca(UO)O(OH)·8HO, were studied by means of theoretical solid-state calculations based on density functional theory using plane waves and pseudopotentials. The positions of the hydrogen atoms in the unit cell of becquerelite mineral were optimized theoretically since it was not possible to determine them from X-ray diffraction data by structure refinement. The structural results, including the lattice parameters, bond lengths and X-ray powder pattern, were found to be in excellent agreement with their experimental counterparts.

Periodic Density Functional Theory Study of the Structure, Raman Spectrum, and Mechanical Properties of Schoepite Mineral.

The structure and Raman spectrum of schoepite mineral, [(UO)O(OH)]·12HO, was studied by means of theoretical calculations. The computations were carried out by using density functional theory with plane waves and pseudopotentials. A norm-conserving pseudopotential specific for the U atom developed in a previous work was employed.

Study of the thermal stability of studtite by in situ Raman spectroscopy and DFT calculations.

The design of a safe spent nuclear fuel repository requires the knowledge of the stability of the secondary phases which precipitate when water reaches the fuel surface. Studtite is recognized as one of the secondary phases that play a key-role in the mobilization of the radionuclides contained in the spent fuel. Thereby, it has been identified as a product formed under oxidation conditions at the surface of the fuel, and recently found as a corrosion product in the Fukushima-Daiichi nuclear plant accident.