B. K. Mani

Scaling law for electrocaloric temperature change in antiferroelectrics.

A combination of theoretical and first-principles computational methods, along with experimental evidence from the literature, were used to predict the existence of a scaling law for the electrocaloric temperature change in antiferroelectric materials. We show that the temperature change scales quadratically with electric field, allowing a simple transformation to collapse the set of ΔT(E) onto a single curve. This offers a unique method that can be used to predict electrocaloric behavior beyond the limits of present measurement ranges or in regions where data are not yet available.

Electrocaloric effect in ferroelectric nanowires from atomistic simulations.

Electrocaloric effect is presently under active investigation owing to both the recent discoveries of giant electrocaloric effects and its potential for solid state cooling applications. We use first-principles-based direct simulations to predict the electrocaloric temperature change in ferroelectric ultrathin nanowires. Our findings suggest that in nanowires with axial polarization direction the maximum electrocaloric response is reduced when compared to bulk, while the room temperature electrocaloric properties can be enhanced by tuning the ferroelectric transition temperature. The potential of ferroelectric nanowires for electrocaloric cooling applications is discussed.

Electric dipole polarizability of alkaline-earth-metal atoms from perturbed relativistic coupled-cluster theory with triples

The perturbed relativistic coupled-cluster (PRCC) theory is applied to calculate the electric dipole polarizabilities of alkaline Earth metal atoms. The Dirac-Coulomb-Breit atomic Hamiltonian is used and we include the triple excitations in the relativistic coupled-cluster (RCC) theory. The theoretical issues related to the triple excitation cluster operators are described in detail and we also provide details on the computational implementation. The PRCC theory results are in good agreement with the experimental and previous theoretical results. We, then, highlight the importance of considering the Breit interaction for alkaline Earth metal atoms.

Tailoring properties of ferroelectric ultrathin films by partial charge compensation

Partial charge compensation in ferroelectric nanostructures is known to play a critical role in stabilizing equilibrium domain patterns. We use first-principles-based simulations to study the effect of partial charge compensation on the response of polarization to the electric field in PbTiO3 and BaTiO3 ultrathin films. Computational data predict that the response can be altered at the qualitative level by tailoring partial charge compensation. We report an unusual transition from ferroelectric to antiferroelectric to dielectric behavior induced by the change in the amount of compensating charge. Interestingly, films with antiferroelectric features exhibit superior potential for energy storage applications.

Relativistic coupled-cluster calculations of N 20 e , A 40 r , K 84 r , and X 129 e : Correlation energies and dipole polarizabilities

We have carried out a detailed and systematic study of the correlation energies of inert gas atoms Ne, Ar, Kr, and Xe using relativistic many-body perturbation theory and relativistic coupled-cluster theory. In the relativistic coupled-cluster calculations, we implement perturbative triples and include these in the correlation energy calculations. We then calculate the dipole polarizability of the ground states using perturbed coupled-cluster theory.

Emergence of ferroelectricity in antiferroelectric nanostructures

First-principles-based finite-temperature simulations are used to predict the emergence of ferroelectricity in antiferroelectric nanostructures made of PbZrO3. The phenomenon is expected to occur in antiferroelectric nanodots, nanowires, and thin films with good surface charge compensation and can be explained by the recently proposed surface effect. Our computations provide a microscopic insight into the equilibrium phases, phase competition, and electrical properties of PbZrO3 nanostructures. The dependence of these properties on the electrical boundary conditions and nanostructure size is investigated.

Triple excitations in perturbed relativistic coupled-cluster theory and electric dipole polarizability of group-IIB elements

We use perturbed relativistic coupled-cluster (PRCC) theory to compute the electric dipole polarizabilities

Perturbed coupled-cluster theory to calculate dipole polarizabilities of closed-shell systems: Application to Ar, Kr, Xe, and Rn

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Atomic properties calculated by relativistic coupled-cluster theory without truncation: Hyperfine constants of Mg + , Ca + , Sr + , and Ba +

of Zn, Cd and Hg. The computations are done using the Dirac-Coulomb-Breit Hamiltonian with Uehling potential to incorporate vacuum polarization corrections. The triple excitations are included perturbatively in the PRCC theory, and in the unperturbed sector, it is included non-perturbatively. Our results of

The role of mechanical boundary conditions in the soft mode dynamics of PbTiO3.

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