Plane-wave pseudopotential total energy calculations have been applied to investigate the structure and energetics of the Cs/K exchange into interlayer sites in muscovite mica. Novel muscovite structures were designed to isolate the effects of 2:1 layer charge, cation size/interlayer site shape, and tetrahedral Al/Si substitutions on the exchange. All atom and cell-parameter optimizations were performed with the intention to mimic the constant pressure, non-isovolumetric exchange conditions thought to be found at frayed-edge sites. Under conditions where the cell parameters are allowed to relax, the overall Cs/K exchange reaction is surprisingly close to isoenergetic. The forward reaction is more strongly favored with increasing layer charge. For the condition of zero layer charge and no interlayer site distortion, the difference in the optimal interlayer spacing for Cs relative to K is very small, indicating a baseline indifference of the muscovite structure to cation size. The presence of 2:1 layer charge or tetrahedral rotations arising from Al/Si substitutions clearly change this outcome. Analysis of the dependence of the interlayer spacing on layer charge shows that while the spacing collapses with increasing layer charge for K as the interlayer cation, the reverse is true for Cs. We attribute the contrasting behavior to inherent differences in the ability of these cations to screen 2:1 layer-layer repulsions. Such effects might be involved during exchange at frayed-edge sites where interlayer spacings are increased. This is known, from experiment, to be very selective for Cs. Overall, the exchange energetics are so low that the Cs/K exchange rate and degree of irreversibility are likely to be dominated by diffusion kinetics.

The atomic structure of dioctahedral 2:1 phyllosilicate edge surfaces was calculated using pseudopotential planewave density functional theory. Bulk structures of pyrophyllite and ferripyrophyllite were optimized using periodic boundary conditions, after which crystal chemical methods were used to obtain initial terminations for ideal (110)- and (010)-type edge surfaces. The edge surfaces were protonated using various schemes to neutralize the surface charge, and total minimized energies were compared to identify which schemes are the most energetically favorable. The calculations show that significant surface relaxation should occur on the (110)-type faces, as well as in response to different protonation schemes on both surface types. This result is consistent with atomic force microscopy observations of phyllosilicate dissolution behavior. Bond-valence methods incorporating bond lengths from calculated structures can be used to predict intrinsic acidity constants for surface functional groups on (110)- and (010)-type edge surfaces. However, the occurrence of surface relaxation poses problems for applying current bond-valence methods. An alternative method is proposed that considers bond relaxation, and accounts for the energetics of various protonation schemes on phyllosilicate edges.

An ab initio theoretical approach has been used to calculate optimized geometries and the relative energies of various compositional arrangements in structures of dioctahedral smectites based on models consisting of two unit-cells. These calculations indicate that the energy differences between structures having vacancies in sites with cis- or trans-OH coordination are small and that their relative energies vary with the chemical nature of the substitutions. For example, a cis-OH coordination for the vacancy was the most stable when the interlayer charge originated from substitution of Al for Si in the tetrahedral sheet, whereas the trans-coordination was the more stable for most cases of substitution in the octahedral sheet, an exception being Fe(II) for Al where the cis-OH coordination was favored. It seems likely, therefore, that long-range structural disorder will be a common phenomenon in natural phyllosilicate specimens.

Highly accurate IR line lists are ready for 13 CO2 isotopologues and 7 SO2 isotopologues. Ames-296K IR lists carry 0.01 - 0.03 cm−1 accuracy up to 13,000 cm−1 for CO2 and 5500 cm−1 for SO2, and 90–95% intensity agreement for most observable bands. Good for atmospheric modeling on Venus and Exoplanets.

The structure of Cs2AlF5 obtained by thermal dehydration of Cs2AlF5•H2O is determined ab initio from powder diffraction data, space group Pmn21, a = 6.36216 (17) Å, b = 12.7523 (4) Å, c = 11.4102 (3) Å, and Z = 6. Contrarily to most A2MF5 compounds presenting MF5cis or trans-chains of corner-sharing MF6 octahedra, Cs2AlF5 is characterized by the rare occurrence of the face-sharing anion Al2F93− combined with an isolated AlF63− octahedron, the sum leading to Al3F156−. The structure of Cs3Al2F9 [space group P63/mmc, a = 6.2535 (2) Å, c = 14.7193 (6) Å, Z = 2] is confirmed to be isostructural with Cs3Fe2F9, built up from the same M2F93− dimers (M = Fe, Al). Both crystal structures are optimized by energy minimization density funtional theory (DFT) in the solid state using a hybrid PBE0 functional, and their relations with the hexagonal perovskites and elpasolites are discussed.

High-resolution neutron powder diffraction (NPD) data were recorded on a series of cathode material LiFe1−xMnxPO4 (x = 0, 0.2, 0.5, 0.8, and 1.0) solid solutions using the HRPD machine at SINQ/PSI, Switzerland. Ab initio crystal structure solution via program FOX indicates demonstrably that the space group of LiFePO4 is Pnma with Li1+ occupying octahedral (4a) sites and Fe2+ octahedral (4c) sites, respectively, in the olivine structure. Rietveld refinement (program FullProf suite version July-2011), complementary with X-ray diffraction data, shows that Fe2+ may partially (about 2%) distribute over Li1+ sites. NPD data for LiFe1−xMnxPO4 (x = 0, 0.2, 0.5, 0.8, and 1.0) reveal that the Mn2+ replaces Fe2+ at the octahedral (4c) sites. The cell parameters a, b, and c increase linearly and the interatomic distances (in Å) of Li–O(2) and Li–O(1) increase, while the interatomic distances (in Å) of Li–O(3) decrease on the addition of Mn, respectively, partially explaining a higher potential plateau of ~4.1 eV in LiMnPO4 compared to ~3.5 eV in LiFePO4.

The structures of γ- and δ-K4P2O7 are solved by X-ray powder diffraction (conventional laboratory X-ray and synchrotron data, respectively), both in hexagonal symmetry (aγ = 5.9645(3) Å, cγ = 14.4972(8) Å, Vγ = 446.64(4) Å3 at 300 °C, Zγ = 2, space group P63/mmc; aδ = 10.211 45(7) Å, cδ = 42.6958(4) Å, Vδ = 3855.59(7) Å3 at room temperature, Zδ = 18, space group P61) with cell–supercell relations $a_\delta \approx a_\gamma \sqrt{3}$ and cδ ≈ 3 cγ. In the experimental conditions, the expected β/γ transition previously announced at 486 °C is not observed; the γ-form is stable at least up to the maximum temperature of our measurements (700 °C). In the γ-form, similar to the orthorhombic form of Na4P2O7, idealized, the pyrophosphate group is in eclipsed conformation, the K+ cations occupying three different coordinations. In the δδ-form, two of the three different [P2O7]4− groups are staggered and one eclipsed, the K+ cations occupying 12 independent sites.

The structure of Ba7Cl2F12 has been determined ab initio from conventional X-ray powder diffraction data by the “heavy atom” method. The cell is hexagonal (space group P6¯, Z=1), with a=10.6373(2) Å and c=4.1724(2) Å. Refinement of 38 parameters by the Rietveld method, using 278 reflections, leads to cRwp=0.173, cRp=0.135, and RB=0.054. The structure has common characteristics with that of the other BaF2-rich fluorochloride, Ba12Cl5F19. In both phases Ba2+ ions lie in tricapped trigonal prisms formed by nine halide ions, and Cl− ions occupy the center of trigonal prisms of Ba2+ ions. F− ions are located in cationic tetrahedra or square pyramids.

An orthorhombic fully ordered structural model is proposed for vaterite [space group Ama2, a=8.4721(5) Å, b=7.1575(7) Å, c=4.1265(4) Å, Z=4, and V=250.23(4) Å3]. It is based on a microtwinning hypothesis, with three domains rotated by 120° along the orthorhombic a axis, regenerating a pseudohexagonal habit. The solution came from direct space ab initio calculations applied to the powder diffraction data. However, five weak superstructure reflections seen in single-crystal and powder diffraction experiments, leading to a six times larger unit cell, are still unexplained.

The structure of 3,4-diaminopyridin-1-ium dihydrogen phosphate, [C5H3(NH)(NH2)2]+ (H2PO4)−, is solved from conventional X-ray powder diffraction data in direct space (monoclinic unit cell with a = 16.0725(9) Å, b = 7.7301(3) Å, c = 14.6189(9) Å, β = 96.869(1)°, V = 1803.2(2) Å3, Z = 8, and space group I2/c), and optimized by energy minimization in the solid state. In the crystal structure of the title compound, dihydrogenphosphate tetrahedra are linked by strong hydrogen O-H…O bonds forming chains running parallel to the b-axis. Antiparallelly π–π stacked DAP cations form molecular columns in the spaces between the chains. Although the dominant interaction of the molecules with their surroundings is electrostatic, their bonding are further enhanced by N-H…O and C-H…O hydrogen bonds.

The structure of bethanechol chloride C7H17ClN2O2 is solved from conventional X-ray powder diffraction data in direct space [monoclinic unit cell with a=8.8749(3) Å, b=16.4118(7) Å, c=7.1373(3) Å, β=93.803(1)°, V=1037.29(7) Å3, Z=4, and space group P21/n]. The existence of a second orthorhombic closely related form is discussed.

[Zr2F8(dmso)2(H2O)2], a dehydration product of [ZrF4(dmso)(H2O)2]⋅2H2O, crystallizes in the orthorhombic symmetry [space group Cmca, a=7.8266(3) Å, b=13.5847(5) Å, c=15.6119(6) Å, and Z=4]. The structure, solved ab initio in direct space from X-ray powder diffraction data, is built up from [Zr2F8O4] bipolyhedra formed by edge sharing of [ZrF5O2] pentagonal bipyramids (condensed from isolated [ZrF4O3] pentagonal bipyramids in the precursor). Difficulties associated with a fortuitous hexagonal pseudosymmetry were surmounted. The dmso departure at 220 °C leads to an amorphous phase.

θ-KAlF4 is a new nanosized potassium tetrafluoroaluminate metastable polymorph (13×18×55 nm3). The crystal structure is solved ab initio from X-ray powder diffraction data in direct space [orthorhombic unit cell with a=8.3242(3) Å, b=7.2502(3) Å, c=11.8875(4) Å, V=717.44(5) Å3, Z=8, and space group Pnma]. This new structure type, unique in the whole AIMIIIF4 family, is related to the fluorite structure and consists of AlF6 octahedra linked via a common edge forming a bioctahedral motif which is trans-connected through the corner-shared fluorine, resulting in the formation of infinite ladderlike double file of octahedra ([Al2F8]2−)n running along the b axis.

La première étape de ce travail est le calcul ab initio des énergies de mise en solution et de mélange du chrome et du fer. Nous confirmons les résultats ab initio proposés précédemment. Nous utilisons cette même méthodologie afin de calculer les énergies de surface du fer et du chrome dans les orientations (100), (110), (111) et (211). Contrairement aux extrapolations depuis les mesures expérimentales aux hautes températures, ces calculs montrent que les énergies de surface du chrome sont supérieures à celles du fer. Nous calculons également l’énergie de ségrégation d’impureté du chrome dans le fer (100) qui est endothermique. Enfin, nous proposons un modèle énergétique ajusté sur les calculs ab initio. À partir de ce modèle, nous calculons des isothermes de ségrégation et montrons que les surfaces de l’alliage sont toujours appauvries en chrome du fait de la grande différence d’énergie de surface entre les deux éléments qui a été révélée par les calculs ab initio.

Data mining of crystal structure databases is performed with methods using deduction, semiempirical heuristic principles, or artificial intelligence to create new information from crystal structure data. In this article, enlightening examples, ranging from a systematic search for new ferroelectric materials to ultrahard, ductile, or high-dielectric-permittivity materials, are detailed, with numerous references providing a handle on the state of the art. This activity is just leaving infancy, especially for its ab initio aspects, with the brightest future ahead. Data mining will clearly guide expensive experiments through inexpensive computations for decades to come. This perspective greatly enhances the value of structure data patiently archived within crystal structure databases for nearly a century now.

The prediction of crystal structure is a key outstanding problem in materials science and one that is fundamental to computational materials design. We argue that by combining the predictive accuracy of quantum mechanics with data mining tools to extract knowledge from a large body of historical experimental or computational results, this problem can be successfully addressed.

Although density functional theory (DFT) calculations have been widely used in many areas of the geosciences for the last 15 years, arguably the most successful application of these methods has been when they are used to understand the properties of minerals and melts in the Earth's pressures of the Earth's 6000 K and 360GPa) are so extreme that experiments under these conditions are very difficult. DFT calculations have been used to provide invaluable estimates of physical parameters that are fundamental to understanding the dynamics and evolution of the Earth. In particular, DFT calculations have helped provide estimates of the mineralogy and chemistry of the Earth's core, the high-temperature and pressure elasticity of the stable crystal phases in the mantle, the effect of defects on physical properties of mantle minerals, and, most recently, the discovery of a new phase of (Mg, Fe)SiO3 just above the core. These and other applications of DFT in the geosciences are described and their implications discussed.