Computational Condensed Matter Physics (CCMP) Group at UARK

Some very recent studies:

"Properties of ferroelectric nanodotsembedded in a polarizable medium: Atomistic simulations", S. Prossandeev and L. Bellaiche, Phys. Rev. Lett. 97, 167601 (2006)

Temperature-versus-Dk phase diagram of a 12x12x12 AB''O3 dot embedded in a AB'O3 medium within a 16x16x16 periodic supercell.The positive Dk part of this diagram corresponds to a soft ferroelectric dot immersed in a medium that is ferroelectrically harder than the dot and that has a decreasing ferroelectric instability as Dk increases. The negative Dk part of this diagram corresponds to a dot (having a ferroelectric instability that is weaker than those of the medium and that decreases, and then vanishes, as Dk increases in magnitude) embedded in a ferroelectrically-soft medium. The lines with symbols represent the phases’ boundaries. The insets show a (001) cross-section of the dipole configuration in the different phases. Specifically, these insets correspond to atomistic calculations with the following (Dk, temperature) combination: (-0.0212 a.u., 1K), (-0.0212 a.u., 500K), (0.0062 a.u., 1K), (0.0087 a.u., 1 K) and (0.0112 a.u., 1K) for the FE3, FE2, FE1, FE1+FT and FT phases, respectively. The dot surfaces are indicated via thick continuous lines in these insets. The x- and y-axes are chosen along the pseudo-cubic [100] and [010] directions, respectively.

"Phase diagram of Pb(Zr,Ti)O3 solid solutions from first principles", Igor A. Kornev, L. Bellaiche, P.-E. Janolin, B.Dkhil, and E. Suard, Phys. Rev. Lett. 97, 157601 (2006)

Phase diagram of Pb(Zr_1-xTi_x)O₃ near its MPB, as predicted by the present scheme with an applied pressure of −4.68 GPa. Symbols display the direct results of our simulations, while lines are guide for the eyes. Indices 1, 2 and 3 indicate the multiphase points. The uncertainty on the transition temperatures is typically around 13K, except close to the multiphase points 2 and 3 for which this uncertainty is around 3K.

"Influence of the growth direction on properties of ferroelectric ultrathin films", I. Ponomareva and L. Bellaiche, Phys. Rev. B 74, 064102 (2006)

Cartesian components of the ground-state spontaneous polarization in Pb(Zr_0.4Ti_0.6)O₃ (~ 46–48-Å-thick) films as a function of the screening coefficient b and expressed in the xyz coordinate system, when choosing 16 and 24 unit cells for the periodicity of the (in-plane) x' and y' directions for [110] and [111] films under compressive strain and 12 unit cells for the periodicity of the x' and y' directions for all other films (see text for the definition of the xyz and x'y'z' coordinate systems). Parts (a), (b), and (c): [001] films under stress free, 2.65% tensile strain, and −2.65% compressive strain, respectively. Parts (d)–(f): same as parts (a)–(c) but for a [110] film. Parts (g)–(i): same as parts (a)–(c) but for a [111] film. The vertical lines characterize the transition of the dipoles pattern from short-circuit-like conditions to open-circuit-like conditions. The schematization of these two different patterns is given above each part. The width of the stripe domains is given in Å.

"Controlling Toroidal Moment by Means of an Inhomogeneous Static Field: An Ab Initio Study", S. Prossandeev, I. Ponomareva, I. Kornev, I. Naumov, and L. Bellaiche, Phys. Rev. Lett. 96, 237601 (2006)

Schematization of the two set-ups considered in this study, the
resulting inhomogeneous electric fields at the sites of the dot and the ground-state dipole pattern.

Dependency of the Cartesian components of the ground-state toroidal moment and polarization (in the top inset) on the angle of rotation about the x-axis of the dipolar source associated with the setup of Fig. (a). For each angle, the calculations are first performed at high temperature and then slowly cooled down until 1 K. The bottom inset reports the dependency of the ground-state toroidal moment for the setup of Fig. (b) (for which no polarization exists) with respect to the angle of rotation about the x-axis of the two dipolar sources.

"Ferroelectricity of perovskites under pressure", I.A. Kornev, L. Bellaiche, P. Bouvier, P.-E. Janolin, B. Dkhil, and J. Kreisel, Phys. Rev. Lett. 95, 196804 (2005)

Electronic-related properties of PbTiO₃ under pressure. Panels (a), (b) and (c) display the partial electronic density of occupied states in the cubic phase at 3.6, 40 and 103 GPa, respectively, for the O 2s, O 2p and Ti 3d orbitals. The zero in energy is chosen at the top of the valence band. Panels (d), (e) and (f) show the electronic charge density of the valence bands located between -22 and -15 eV in the vertical (100) plane passing through Ti (center), O_parallel (top and bottom sides), and O_perpend (left and right sides) atoms for the cubic state at 3.6, 40, and 103 GPa, respectively. Panels (g)-(i) display the same information as Panels (d)-(f), respectively, but for the P4mm equilibrium - for which Ti moves towards the bottom oxygen atom.

"Electric-field induced domain evolution in ferroelectric ultrathin films ,'' Bo-Kuai Lai, I Ponomareva, I. I. Naumov, Igor A. Kornev, Huaxiang Fu, L. Bellaiche and G. J.Salamo, Phys. Rev. Lett. 96, 137602 (2006)

Nanobubbles in ferroelectric ultrathin films under external electric field.

Yellow lines indicate plane of y=8, which cross-sectional view is shown in inset.

"Atomistic treatment of depolarizing energy and field in ferroelectric nanostructures", I. Ponomareva, I. I. Naumov, I. Kornev, H. Fu, and L. Bellaiche, Phys. Rev. B 72, 140102 (2005)

(a) Dipole moments and (b) toroid moment of polarization in a PZT nanodot as a function of the screening coefficient β. Insets of (a) and (b) show the polarization pattern for β=1 (ideal short circuit conditions) and β=0 (ideal open circuit conditions), respectively.

CCMP web page: Inna Ponomareva

Last updated : 25th October, 2007