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Computational Condensed Matter Physics (CCMP) Group
University of Arkansas
We carry research
in the field of computational condensed matter physics. Our current interests
mainly lie in developing and/or using direct first-principles methods,
first-principles-based techniques and semiempirical approaches to calculate
properties of ferroelectrics, magnetic compounds, multiferroics,
semiconductors and nanostructures.
Some recent studies:
''Nature of
dynamical coupling between polarization and strain in nanoscale ferroelectrics
from first principles,''
I. Ponomareva
and L. Bellaiche, Physical Review Letters 101, 197602 (2008).
Snapshots
at different times of a (x,y) cross-section of the dipole pattern in a PZT
film initially possessing low-density nanobubbles (Pattern III). This
cross-section corresponds to the most inner (001) B-plane, and the x- and
y-axis lie along the [100] and [010] directions, respectively. Red
(respectively, blue) areas show areas with dipoles pointing ''up'' (respectively,
''down'') along the z-direction. These data correspond to the intermediate
strain pulse (dashed lines in Fig.1 (a) and (c)), and an initial nanobubble volume
of 5.3 nm3.
''Controlling
double vortex states in
low-dimensional dipolar systems,''
S. Prosandeev
and L. Bellaiche, Physical Review Letters 101, 097203 (2008).
Schematization
of the dipole arrangement in a (x, y)
plane for magnetic states playing a key role in the reversal of the
hypertoroidal moment. Crosses represent the vortex centers.
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''Coexistence
of the Phonon and Relaxation Soft Modes in the Terahertz Dielectric Response
of Tetragonal BaTiO3,''
J. Hlinka, T.
Ostapchuk, D. Nuzhnyj, J. Petzelt, P. Kuzel, C. Kadlec, P. Vanek, I.
Ponomareva and L. Bellaiche, Physical Review
Letters bf 101, 167402 (2008).
Dipole moment pz of
an arbitrarily chosen unit cell as a function of time in MD simulations at
T=TC-10K. The inset shows the 8 possible off-center Ti sites. The
Ti ion mostly fluctuates around and among the 4 sites preferred by the
molecular field (full circles, pz> 0). Occasionally, it also
hops towards the excited site (dashed circles, pz<0).
These hops correspond to the few
negative spikes encountered on the pz trajectory.
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"Control
of vortices by homogeneous fields in asymmetric low-dimensional dipolar
systems,"
S. Prosandeev, I. Ponomareva, I. Kornev, and L. Bellaiche, Phys. Rev.
Lett. 100, 047201 (2008).
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Predicted
hysteresis loops in asymmetric ferromagnetic rings [Panels (a) and (b)] and
in asymmetric ferroelectric rings [Panels (c) and (d)]. Panels (a) and (b)
display the behavior of the magnetization and magnetic toroidal moment,
respectively, as a function of the applied homogeneous ac magnetic field. Panels
(c) and (d) show the evolution of the polarization and electric toroidal
moment, respectively, versus the applied homogeneous ac electric field.
Insets schematize the rings' geometry and the dipole arrangement in the
(x,y) plane for eight important states: vortex states (states (1), (3),
(5), and (7)), onion states (states (2) and (4)), and antiferrotoroidic
pair states (states (6) and (8)).
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External
dielectric susceptibility χext of a PZT60 film [part (a)],
wire [part (b)], and dot [part (c)] vs the screening parameter β. Left
and right insets show the projections of the dipole patterns in the structures
under open-circuit-like and short-circuit-like boundary conditions,
respectively. The vertical lines characterize the transition from
short-circuit-like conditions to open-circuit-like conditions.
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Internal
dielectric susceptibility χint of a PZT60 film [part
(a)], wire [part (b)], and dot [part (c)] vs the screening parameter
β. The vertical lines characterize the transition from
short-circuit-like conditions to open-circuit-like conditions. Note
that χintxx(yy)=χextxx(yy)
in the film, while χintzz=χextzz
in the wire - since no depolarizing field exists along these
directions.
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"Terahertz
dielectric response of cubic BaTiO3,"
I. Ponomareva, L. Bellaiche, T. Ostapchuk, J. Hlinka and J. Petzelt, Phys.
Rev. B 77, 012102 (2008).
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Complex
dielectric response of cubic BaTiO3 versus frequency at
T=440 (bold lines) and 470 K (thin lines). Panels (a) and (b) displays
the ε' real and ε'' imaginary parts, respectively. Solid
lines show our predictions, while the dashed lines report our
measurements. Arrows emphasize the frequencies of the two peaks of
ε''.
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Real-space
decomposition, χ''(ν=ν'i,x,y,z=0)/(ε''(ν=ν')-1)
(for i=1 and 2, expressed in percent and for three different
temperatures), of the two peaks of the imaginary part of the dielectric
constant. The x, y and z-axes are chosen along the [100], [010] and
[001] directions, respectively, and their coordinates are expressed in
terms of the 5-atom unit cell lattice's constant (that is, a=0.39 nm).
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"Properties
of ferroelectric nanodots embedded in a polarizable medium: Atomistic
simulations",
S. Prossandeev and L. Bellaiche, Phys. Rev. Lett. 97,
167601 (2006)
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 Temperature-versus-Δκ phase
diagram of a 12x12x12 AB''O3 dot embedded in a AB'O3 medium within a
16x16x16 periodic supercell.The positive Δκ 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 Δ&kappa increases. The negative
Δκ 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 Δκ 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 (Δκ 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.
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"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)
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Phase
diagram of Pb(Zr1-xTix)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.
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"Influence
of the growth direction on properties of ferroelectric ultrathin
films",
I. Ponomareva and L. Bellaiche, Phys. Rev. B 74,
064102 (2006)
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Cartesian
components of the ground-state spontaneous polarization in Pb(Zr0.4Ti0.6)O3
(4.6-4.8-nm-thick) films as a function of the screening coefficient β
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 Angstrom.
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"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.
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Electronic-related
properties of PbTiO3under 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), Oparallel (top and bottom
sides), and Operpend (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.
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"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).
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"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.
CCMP web page: Wei
Ren
Last updated : 07 Jan, 2009
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