The full phonon dispersion relations of lead titanate and zirconate in the cubic perovskite structure are computed using first-principles variational density-functional perturbation theory, with ab initio pseudopotentials a plane-wave basis set. Comparison results previously obtained for barium shows that change single constituent (Ba to Pb, Ti Zr) has profound effects on character unstable modes, significant implications nature phase transitions dielectric piezoelectric responses compounds....

Topological defects can affect the physical properties of graphene in unexpected ways. Harnessing their influence may lead to enhanced control both material strength and electrical properties. Here we present a new class topological composed rotating sequence dislocations that close on themselves, forming grain boundary loops either conserve number atoms hexagonal lattice or accommodate vacancy/interstitial reconstruction, while leaving no unsatisfied bonds. One loop is observed as "flower"...

We have determined the electronic and atomic structure of N doped TiO2 using a combination hard x-ray photoelectron spectroscopy first-principles density functional theory calculations. Our results reveal that doping leads to formation oxygen vacancies both impurity accounts for observed visible light catalytic behavior TiO2.

${\mathrm{CaTiO}}_{3}$ has a static dielectric constant that extrapolates to value greater than 300 at zero temperature. We investigate the origin of this large response on microscopic level, using first-principles plane-wave pseudopotential density functional theory calculations. The electronic tensor and complete set zone center phonons ionic Born effective charges are determined for in its low temperature 20-atom per cell orthorhombic phase via frozen phonon structure, polarization, force...

Molecular-dynamics simulations of a first-principles Hamiltonian for the model relaxor ferroelectric were used to determine nature correlations between chemical and polar short-range order. Relative chemically disordered regions (CDRs), ordered (CORs) exhibit enhanced polarization, polarization fluctuations at all temperatures. Magnitudes pairwise cluster-cluster follow trend COR-COR, COR-CDR, CDR-CDR correlations. This result implies that characteristic lengthscale nanoregions is same as

Molecular dynamics simulations of first-principles-based effective Hamiltonians for $\mathrm{Pb}({\mathrm{Sc}}_{1/2}{\mathrm{Nb}}_{1/2}){\mathrm{O}}_{3}$ under hydrostatic pressure and $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$ at ambient show clear evidence a relaxor state in both systems. The Burns temperature is identified as the below which dynamic nanoscale polar clusters form, pinned to regions quenched chemical short-range order. effect demonstrates that...

The development of sorbents for next-generation CO(2) mitigation technologies will require better understanding CO(2)/sorbent interactions. Among the under consideration are shape-selective microporous molecular sieves with hierarchical pore morphologies reduced dimensionality. We have characterized non-equilibrium sorption OMS-2, a well-known one-dimensional octahedral sieve manganese oxide framework. Remarkably, we find that degree hysteresis increases when gas/sorbent system is allowed to...

First principles density functional theory DFT+U calculations and experimental neutron diffraction structure analyses were used to determine the low-temperature crystallographic magnetic of bixbyite Mn2O3. The energies various arrangements, calculated from first principles, fit a cluster-expansion model using Bayesian method that overcomes problem underfitting caused by limited number input configurations. was predict lowest-energy states. Experimental determination benefited optimized...

Lattice dynamics for five ordered ${\mathrm{PbMg}}_{1∕3}{\mathrm{Nb}}_{2∕3}{\mathrm{O}}_{3}$ supercells were calculated from first principles by the frozen phonon method. Maximal symmetries of all are reduced structural instabilities. modes corresponding to these instabilities, equilibrium ionic positions, and infrared reflectivity spectra computed supercells. Results compared with our experimental data a chemically disordered PMN single crystal.

Local structures in BaTi${}_{1\ensuremath{-}x}$Zr${}_{x}$O${}_{3}$ solid solutions were analyzed using x-ray absorption fine structure (XAFS) measurements and density-functional theory (DFT) calculations. We demonstrate that for low concentrations of Ti, isolated Ti atoms the relatively large octahedral sites BaZrO${}_{3}$ lattice acquire centrosymmetric coordination with average Ti-O distances shorter than those BaTiO${}_{3}$. In contrast higher having one or more as their B-site nearest...

Shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) and density functional theory (DFT) are used to probe Cl– adsorption the order–disorder phase transition associated with c(2 × 2) adlayer on Cu(100) in acid media. A two-component ν(Cu–Cl) vibrational band centered near 260 ± 1 cm–1 is track potential dependence of adsorption. The dominant component tracks coverage fluctional terraces good agreement normalized intensity superstructure rods prior surface X-ray diffraction...

Plane-wave pseudopotential calculations of total energies were performed for three ordered perovskite related supercells in each the eight stoichiometries ${A(B}_{1/3}{B}_{2/3}^{\ensuremath{'}}){\mathrm{O}}_{3};$ $A=\mathrm{P}\mathrm{b},\mathrm{}\mathrm{Ba},B=\mathrm{Z}\mathrm{n},\mathrm{}\mathrm{Mg}$ and, ${B}^{\ensuremath{'}}=\mathrm{N}\mathrm{b},\mathrm{T}\mathrm{a};$ and ${A(B}_{1/2}{B}_{1/2}^{\ensuremath{'}}){\mathrm{O}}_{3};$ $B=\mathrm{S}\mathrm{c},\mathrm{I}\mathrm{n}.$ A striking...

We propose a structural model for decagonal Al-Cu-Co quasicrystals based upon existing experimental diffraction data supplemented by total energy calculations. The is decoration of tiles related to the Penrose rhombus tiling. Strong chemical ordering between Cu and Co leads chains alternating atoms. These project onto tile edges, where they define arrows. At low temperatures, interatomic potentials lead rules fixing relative orientation majority are subset matching rules.

Quasicrystals are metal alloys whose noncrystallographic symmetries challenge traditional methods of structure determination. We employ quantum-based total-energy calculations to predict the a decagonal quasicrystal from first-principles considerations. Our Monte Carlo simulations take as input knowledge that phase occurs in Al-Ni-Co near given composition and use limited amount experimental structural data. The resulting obeys nearly deterministic decoration tiles on hierarchy length scales...

Abstract The phenomenology of Pb(B,B′)O3 perovskite-based relaxor ferroelectrics (RFE) is reviewed, with emphasis on the relationship between chemical short-range order and formation polar nanoregions in temperature range "freezing" temperature, T f, Burns B. Results are presented for first-principles-based effective Hamiltonian simulations (PSN), that were done empirically modified variants PSN Hamiltonian. Arbitrarily increasing magnitudes local electric fields, caused by an increase...

High-pressure and variable temperature single-crystal synchrotron x-ray measurements combined with first principles based molecular-dynamics simulations were used to study diffuse scattering in the relaxor ferroelectric system ${\text{PbSc}}_{1/2}{\text{Nb}}_{1/2}{\text{O}}_{3}$. Constant experiments show a pressure-induced transition phase, which butterfly- rod-shaped occurs around {h00} {hh0} Bragg spots. Simulations qualitatively reproduce observed features as well their...

We use first-principles density functional theory total energy and linear response phonon calculations to compute the Helmholtz Gibbs free as a function of temperature, pressure, cell volume in flexible metal–organic framework material MIL-53(Cr) within quasiharmonic approximation. GGA metaGGA were performed, each including empirical van der Waals (vdW) forces under D2, D3, or D3(BJ) parametrizations. At all temperatures up 500 K pressures from −30 30 MPa, two minima versus are found,...

The polarization of a nearest-neighbor (nn) Pb-O vacancy pair $[{(V}_{\mathrm{Pb}}\ensuremath{-}{V}_{\mathrm{O}}{)}_{\mathrm{nn}}]$ in ${\mathrm{PbTiO}}_{3}$ is calculated, using the modern theory polarization, implemented density-functional-theory ultrasoft pseudopotential formalism. dipole moment per divacancy, ${\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}}_{{(V}_{\mathrm{Pb}}\ensuremath{-}{V}_{\mathrm{O}}{)}_{\mathrm{nn}}},$ about $2.28e{r}_{\mathrm{nn}},$ where...

Spectroscopic studies involving dielectric, submillimeter, infrared, and Raman measurements were performed on a ${\mathrm{CaTiO}}_{3}$ single crystal, covering broad spectral range (static to 10 THz) at temperatures from 6 300 K. The results show mode softening characteristic of an incipient ferroelectric with ${T}_{c}\ensuremath{\approx}\ensuremath{-}105\mathrm{K}.$ A signature the soft is seen in spectra, even though modes are not active first order. First-principles calculations used...

First-principles calculations were used to study the effects of neutral and $2+$ charged oxygen vacancies on dielectric properties crystalline $\mathrm{Hf}{\mathrm{O}}_{2}$. In agreement with previous results, vacancy is more stable four fold-coordinated site, while a three site. For both positions, $\mathrm{Hf}{\mathrm{O}}_{2}$ remains insulating whether or in charge state. The dynamical matrix, Born effective charges, electronic tensor calculated for each structure. With one per 64 atoms,...

A common approach in computational science is to use a set of highly precise but expensive calculations parameterize model that allows less precise, more rapid on larger scale systems. Least-squares fitting underfits the data generally used for this purpose. For arbitrarily free from statistic noise, e.g. ab initio calculations, we argue it appropriate begin with ensemble models overfit data. Within Bayesian framework, most likely can be defined incorporates physical knowledge, provides...

Abstract We develop a model for Al-Co decagonal quasicrystals and approximants. Our defines large number of potential atomic positions. These sites are populated by two that interact with each other through electronic-structure-based pair potentials. Monte Carlo simulation the produces realistic configurations alloys in temperature composition ranges where metastable quasicrystal exists. The resulting structures generally consist packings space pentagonal bipyramid clusters. Projections...

By exploiting the periodic cells which are approximants to icosahedral phase, problem of structure determination phase can be converted standard crystallographic refinement problem. As larger used, structures obtained converge that phase. We refine (hypothetical) 1/1 cubic approximant AlCuFe using this technique, with aim determining