Ethane under pressure revisited using x-ray diffraction, Raman spectroscopy, infrared absorption, and ab initio calculations up to 150 GPa.

Ethane (C2H6) is anticipated to be the most stable compound within the carbon-hydrogen system under the 100 GPa pressure range. Nevertheless, the properties of ethane under pressure are still poorly documented. Here, we present a comprehensive study of the structural and vibrational properties of C2H6 in a diamond anvil cell at pressures up to 150 GPa.

High pressure polymorphism of LiBH and of NaBH.

The pressure-induced structural changes in LiBH and in NaBH have been investigated experimentally up to 290 GPa by coupling Raman spectroscopy, infrared absorption spectroscopy and synchrotron X-ray diffraction. This data set is also analysed in the light of Density Functional Theory calculations performed up to 600 GPa. The [BH] unit appears to be remarkably resistant under pressure.

Structural, electronic and energetic properties of uranium-americium mixed oxides [Formula: see text] using DFT[Formula: see text] calculations.

In this paper, we determine for the first time the electronic, structural and energetic properties of [Formula: see text] mixed oxides in the entire range of Am content using the generalized gradient approximation (GGA)[Formula: see text] in combination with the special quasirandom structure (SQS) approach to reproduce chemical disorder. This study reveals that in [Formula: see text] oxides, Am cations act as electron acceptors, whereas U cations act as electron donors showing a fundamental difference with [Formula: see text] or [Formula: see text] in which there is no cation valence change in stoichiometric conditions compared to the pure oxides. We show for the first time that the lattice parameter of stoichiometric [Formula: see text] follows a linear evolution which is the structural signature of an ideal solid solution behavior.

Isotope effect on hydrogen bond symmetrization in hydrogen and deuterium fluoride crystals by molecular dynamics simulation.

The isotope effect on the collective proton/deuteron transfer in hydrogen and deuterium fluoride crystals has been investigated at 100 K by ab initio quantum-thermal-bath path-integral molecular dynamics (QTB-PIMD) simulation. The deuterons within a planar zigzag chain of the orthorhombic structure simultaneously flip between covalent and hydrogen bonds due to the barrier crossing through tunnelling. The height of the corresponding static barrier normalized for one deuteron is 29.

Site Selectivity of Hydride in Early-Transition-Metal Ruddlesden-Popper Oxyhydrides.

Layered perovskite titanium oxyhydrides have been prepared by low-temperature topochemical CaH reduction from Ruddlesden-Popper Sr Ti O phases ( n = 1, 2) and structurally characterized by combined synchrotron X-ray and neutron diffraction data refinements. In the single-layered SrTiOD material, hydride anions are statistically disordered with oxides on the apical site only, as opposed to known transition-metal oxyhydrides exhibiting a preferred occupation of the equatorial site. This unprecedented site selectivity of H has been reproduced by periodic DFT+ U calculations, emphasizing for the hydride defect a difference in formation energy of 0.

Vacancies and holes in bulk and at 180° domain walls in lead titanate.

Domain walls (DWs) in ferroic materials exhibit a plethora of unexpected properties that are different from the adjacent ferroic domains. Still, the intrinsic/extrinsic origin of these properties remains an open question. Here, density functional theory calculations are used to investigate the interaction between vacancies and 180° DWs in the prototypical ferroelectric PbTiO, with a special emphasis on cationic vacancies and released holes.

Reply to the 'Comment on "Proton transport in barium stannate: classical, semi-classical and quantum regime"'.

We respond to the erroneous criticisms about our modeling of proton transport in barium stannate [G. Geneste et al., Phys.

Simulating the Radio-Frequency Dielectric Response of Relaxor Ferroelectrics: Combination of Coarse-Grained Hamiltonians and Kinetic Monte Carlo Simulations.

The radio-frequency dielectric response of the lead-free Ba(Zr_{0.5}Ti_{0.5})O_{3} relaxor ferroelectric is simulated using a coarse-grained Hamiltonian.

Photostriction in Ferroelectrics from Density Functional Theory.

An ab initio procedure allowing the computation of the deformation of ferroelectric-based materials under light is presented. This numerical scheme consists in structurally relaxing the system under the constraint of a fixed n_{e} concentration of electrons photoexcited into a specific conduction band edge state from a chosen valence band state, via the use of a constrained density functional theory method. The resulting change in lattice constant along a selected crystallographic direction is then calculated for a reasonable estimate of n_{e}.

Photovoltaics with Ferroelectrics: Current Status and Beyond.

Ferroelectrics carry a switchable spontaneous electric polarization. This polarization is usually coupled to strain, making ferroelectrics good piezoelectrics. When coupled to magnetism, they become so-called multiferroic systems, a field that has been widely investigated since 2003.

Proton transport in barium stannate: classical, semi-classical and quantum regimes.

Density-functional theory calculations are performed to investigate proton transport in BaSnO3. Structural optimizations in the stable and saddle point configurations for transfer (hopping) and reorientation allow description of the high-temperature classical and semi-classical regimes, in which diffusion occurs by over-barrier motion. At lower temperature (typically below 300 K), we describe the thermally-assisted quantum regime, in which protonic motion is of quantum nature and occurs in "coincidence" configurations favored by thermal fluctuations of the surrounding atoms.

New iron hydrides under high pressure.

The Fe-H system has been investigated by combined x-ray diffraction studies and total energy calculations at pressures up to 136 GPa. The experiments involve laser annealing of hydrogen-embedded iron in a diamond anvil cell. Two new FeHx compounds, with x∼2 and x=3, are discovered at 67 and 86 GPa, respectively.

A model for multiphoton absorption in dielectric materials induced by short laser pulses at moderate intensities.

We present a semi-analytical model for free electron production induced by multiphoton ionization in dielectric materials for short laser pulses at moderate intensities. Within this approach, the laser-induced absorption is described through the Bloch-Volkov formalism, and the electronic structure of materials is evaluated through first-principles calculations. Results obtained for NaCl and KDP (KH2PO4) materials show that significant deviations from the parabolic band approximation may occur.

Strong isotope effect in phase II of dense solid hydrogen and deuterium.

Quantum nuclear zero-point motions in solid H(2) and D(2) under pressure are investigated at 80 K up to 160 GPa by first-principles path-integral molecular dynamics calculations. Molecular orientations are well defined in phase II of D(2), while solid H(2) exhibits large and very asymmetric angular quantum fluctuations in this phase, with possible rotation in the (bc) plane, making it difficult to associate a well-identified single classical structure. The mechanism for the transition to phase III is also described.

Novel complex phenomena in ferroelectric nanocomposites.

A first-principles-based effective Hamiltonian is used to investigate finite-temperature properties of ferroelectric nanocomposites made of periodic arrays of ferroelectric nanowires embedded in a matrix formed by another ferroelectric material. Novel transitions and features related to flux-closure configurations are found. Examples include (i) a vortex core transition, that is characterized by the change of the vortex cores from being axisymmetric to exhibiting a 'broken symmetry'; (ii) translational mode of the vortex cores; (iii) striking zigzag dipolar chains along the vortex core axis; and (iv) phase-locking of ferroelectric vortices accompanied by ferroelectric antivortices.

Polarization dependent chemistry of ferroelectric BaTiO3(001) domains.

Recent works suggest that the surface chemistry, in particular the presence of oxygen vacancies, can affect the polarization in a ferroelectric material. This should, in turn, influence the domain ordering driven by the need to screen the depolarizing field. Here we show using density-functional theory that the presence of oxygen vacancies at the surface of BaTiO(3)(001) preferentially stabilizes an inward pointing, P-, polarization.

Correlations and local order parameter in the paraelectric phase of barium titanate.

General features of the order parameter distribution in barium titanate in its paraelectric phase and in its ferroelectric phases (tetragonal and orthorhombic) are presented. The density of probability of the polarization [Formula: see text], defined by an average of the local order parameters over regions of various sizes and shapes (L(x) × L(y) × L(z)), is examined by molecular dynamics simulations using a first-principles derived effective Hamiltonian. The free energies [Formula: see text] associated with these probabilities are computed by thermodynamic integration.

Thermodynamics and kinetics of the Schottky defect at terraces and steps on the MgO(001) surface.

The Schottky defects at both the flat MgO(001) surface and the monatomic-step edge have been investigated by equilibrium molecular dynamics simulations. The formation enthalpy as a function of the distance between the Mg and O vacancies that form a Schottky defect have been calculated and discussed. We conclude that a step edge is a stable location for a vacancy.

Atomistic screening mechanism of ferroelectric surfaces: an in situ study of the polar phase in ultrathin BaTiO3 films exposed to H2O.

The polarization screening mechanism and ferroelectric phase stability of ultrathin BaTiO(3) films exposed to water molecules is determined by first principles theory and in situ experiment. Surface crystallography data from electron diffraction combined with density functional theory calculations demonstrate that small water vapor exposures do not affect surface structure or polarization. Large exposures result in surface hydroxylation and rippling, formation of surface oxygen vacancies, and reversal of the polarization direction.

Competing mechanisms in the atomic diffusion of a MgO admolecule on the MgO(001) surface.

The diffusion mechanism of a MgO admolecule on a flat MgO(001) surface has been investigated by equilibrium molecular dynamics simulation. Care has been taken in the choice of the phenomenological interionic potential used. Four distinct mechanisms have been found and the corresponding dynamical barriers determined at high temperature.

Adsorption and diffusion of Mg, O, and O2 on the MgO(001) flat surface.

A thorough investigation of the adsorption and diffusion of Mg, O, and O(2) on MgO(001) terraces is performed by first-principles calculations. The single Mg adatom weakly binds to surface oxygens, diffuses, and evaporates easily at room temperatures. Atomic O strongly binds to surface oxygens, forming peroxide groups.