Interatomic potentials are determined in the framework of a shell model used to simulate structural instabilities, dynamical properties, and phase transition sequence BaTiO3. The is developed from first-principles calculations by mapping potential energy surface for various ferroelectric distortions. parameters obtained performing fit interatomic this surface. Several zero-temperature properties BaTiO3, which central importance, correctly simulated our model. diagram as function temperature...

We report from first-principles-based atomistic simulations that ferroelectricity can be sustained in PbTiO3 nanoparticles of only a few lattice constants size as result toroidal ordering. found size-induced topological transformations lead to the stabilization ferroelectric bubble by alignment vortex cores along closed path. These transformations, which are driven aspect ratio nanostructure, change topology polarization field, producing rich variety polar configurations. For sufficiently...

In this paper, we present the results of electronic structure, ab initio calculations performed on ReO3, WO3, and stoichiometric tungsten bronze NaWO3. We examine relation between structural properties three materials comment solid state chemistry governing interaction transition metal its oxygen ligands. show that off-center displacements W ion in WO3 are driven by onset covalent interactions with nearest oxygen, while metallic ReO3 NaWO3 stable when cubic. latter case, antibonding...

We present a finite-temperature study of ferroelectric phase transitions in ${\mathrm{BaTiO}}_{3}$ ultrathin films using an atomic-level simulation approach. This is based on shell model for with parameters obtained from first-principles calculations. While involving in-plane electric polarization are practically unperturbed by the presence surface, surface atomic relaxations act as strong perturbation order perpendicular to surface. However, strain induced polydomain out-of-plane...

The electronic structure of SrBi2Ta2O9 is investigated from first-principles, within the local density approximation, using full-potential linearized augmented plane wave (LAPW) method. results show that, besides large Ta(5d)-O(2p) hybridization which a common feature ferroelectric perovskites, there an important between bismuth and oxygen states. underlying static potential for distortion primary source ferroelectricity by lattice-dynamics study Frozen Phonon approach.

Classical shell-model potentials for describing the complex ferroelectric behaviour of barium titanate and strontium are developed used to simulate BaxSr1−xTiO3 solid solutions. The temperature versus composition phase diagram is very well described local structure polarization analysed. It shown that properties solution can be understood in terms effects average density chemical environment. experimentally observed static dielectric peak broadening around Tc at low x reproduced simulation...

The Perdew-Burke-Ernzerhof generalized gradient approximation to the density functional theory is tested with respect sensitivity choice of value parameter \ensuremath{\kappa}, which associated degree localization exchange-correlation hole. A study structural and dynamical properties four selected ferroelectric perovskites presented. originally proposed $\ensuremath{\kappa}=0.804$ works well for some solids, whereas $\mathrm{AB}{\mathrm{O}}_{3}$ it must be decreased in order predict...

Atomistic simulations show that there are long-ranged ferroelectric interactions between the layers in ferroelectric/paraelectric superlattices mediated by continuous chains of polarization running through intervening paraelectric layers. The resulting behavior superlattice is strongly dependent on modulation length. At short lengths acts as a single-component system; at long individual act almost independently.

The dynamics of a two-dimensional shell model with double-well potential in the core-shell interaction is simulated by means molecular-dynamics techniques. Snapshots lattice displacement pattern reveal presence precursor regions high-temperature phase, while low-temperature phase dynamical structure factor exhibits quasielastic component addition to ferroelectric soft-mode peak. On other hand, local particles are characterized two different time scales corresponding coexistence interwell and...

The off-centre displacement delta of a Li ion in KTaO3 and the surrounding lattice distortion is calculated using nonlinear shell model developed for pure lattice. method static Green function applied range dipole forces limited to few constants. A short Li-O interaction potential used which leads lithium reasonable agreement with estimations made from NMR measurements. polarisation found develop region around Li, whose total moment exceeds by factor 4.5 that arising itself. This...

The ground-state polarization of BaTiO3 nanosized films and cells is studied using an atomic-level simulation approach based on a shell model with parameters obtained from first-principles calculations. We demonstrate that the critical thickness for ferroelectricity in free-standing stress-free film 3.6 nm, decrease lateral size to nanometric dimensions does not spoil ferroelectric properties film. Nanocells different faces, BaO or TiO2 planes, present domain structure due strong surface effect.

The microscopic origin of ferroelectric instabilities in Aurivillius compounds is investigated from first principles using the full-potential linearized augmented plane-wave method. A comparative study archetype materials like ${\mathrm{Bi}}_{2}{\mathrm{WO}}_{6}$, ${\mathrm{SrBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9}$, and ${\mathrm{Bi}}_{4}{\mathrm{Ti}}_{3}{\mathrm{O}}_{12}$ by a lattice-dynamics paraelectric phase frozen-phonon approach. An analysis different displacement patterns...

Interface effects on the ferroelectric behavior of ${\mathrm{PbTiO}}_{3}$ ultrathin films deposited a ${\mathrm{SrTiO}}_{3}$ substrate are investigated using an interatomic potential approach with parameters fitted to first-principles calculations. We find that correlation atomic displacements across film-substrate interface is crucial for stabilization state in few unit cells thick. show minimum film thickness appearance spontaneous polarized domain not intrinsic property but depends...

We use atomic-level simulation methods to determine the zero-temperature structure and properties of coherent KNbO3/KTaO3 superlattices. find that in-plane behavior is essentially bulk-like with an abrupt jump in polarization at interfaces. By contrast, modulation direction continuous through interfaces interior KTaO3 layers remaining polarized for lengths up 160 unit cells. The zero-frequency dielectric constant has a similar magnitude KNbO3. An investigation switching shows greater than 24...

Electronic-structure calculations are performed, within the local-density approximation to density-functional theory, using full-potential linear muffin-tin orbital method understand relation between structural and electronic properties of ${\mathrm{ReO}}_{3}$ , ${\mathrm{WO}}_{3}$ stoichiometric tungsten bronze ${\mathrm{NaWO}}_{3}$ . Energy changes associated with small deformations from cubic phase indicate that stable when while W ion in shows a tendency off-center displacements. The...

Building on the insights gained from electronic-structure calculations and experience obtained with an earlier atomic-level method, we developed simulation approach based traditional Buckingham potential shell model which correctly reproduces ferroelectric phase behavior dielectric piezoelectric properties of KNbO3. This now enables solid solutions defected systems; illustrate this capability by elucidating a KTa0.5Nb0.5O3 random solution.

The phase transitions and dynamical behavior of superlattices consisting equal-thickness layers a perovskite ferroelectric (KNbO3) paraelectric (KTaO3) are explored using molecular-dynamics simulation. We find that the response in plane modulation direction essentially decoupled. Curie temperature for transition from polarized to unpolarized state decreases approximately linearly with length, Λ, Λ>12; smaller lengths, it is constant. appears be only weakly modulation-length dependent....

Surface and ferroelectric properties of ${\mathrm{PbTiO}}_{3}$ thin films are investigated using an interatomic potential approach with parameters determined from first-principles calculations. We show that a model developed for the bulk describes properly surface ${\mathrm{PbTiO}}_{3}$. In particular, antiferrodistortive reconstruction, recently observed x-ray scattering, is correctly reproduced as result change in balance long-range Coulombic short-range interactions at surface. The...

We report total-energy calculations for different crystal structures of NaNbO${}_{3}$ over a range unit-cell volumes using the all-electron full-potential (linearized) augmented plane-wave method. employed both local-density approximation (LDA) and Wu-Cohen form generalized gradient (GGA-WC) to test accuracy these functionals description complex structural behavior NaNbO${}_{3}$. found that LDA not only underestimates equilibrium volume system but also predicts an incorrect ground state this...

The structural and polar properties of $\mathrm{BiFe}{\mathrm{O}}_{3}$ at finite temperature are investigated using an atomistic shell model fitted to first-principles calculations. Molecular dynamics simulations show a direct transition from the low-temperature $R3c$ ferroelectric phase Pbnm orthorhombic without evidence any intermediate bridging between them. high-temperature is characterized by presence two sublattices with opposite polarizations, it displays characteristic...

The influence of Li impurities on the phase transition sequence KNbO${}_{3}$ is investigated using an atomistic model with parameters fitted to first-principles calculations. We find that replacement K by ions increases local electric dipoles due a large off-centering along [001] directions. doping strongly affects temperatures as result coupling between off-center relaxation dynamics and macroscopic polarization host material. This produces decrease in for rhombohedral-orthorhombic...