Ferroelectric Polarization of CH3NH3PbI3: A Detailed Study Based on Density Functional Theory and Symmetry Mode Analysis

2015 ◽  
Vol 6 (12) ◽  
pp. 2223-2231 ◽  
Author(s):  
Alessandro Stroppa ◽  
Claudio Quarti ◽  
Filippo De Angelis ◽  
Silvia Picozzi
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Ferroelectric Polarization ◽  
Mode Analysis ◽  
Functional Theory ◽  
Symmetry Mode

scholarly journals Current-induced runaway vibrations in dehydrogenated graphene nanoribbons

2016 ◽  
Vol 7 ◽  
pp. 68-74 ◽  
Author(s):  
Rasmus Bjerregaard Christensen ◽  
Jing-Tao Lü ◽  
Per Hedegård ◽  
Mads Brandbyge
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Graphene Nanoribbons ◽  
Electrical Current ◽  
Mode Analysis ◽  
Functional Theory ◽  
Magnetic Current ◽  
Langevin Approach ◽  
Armchair Graphene Nanoribbon ◽  
Armchair Graphene

We employ a semi-classical Langevin approach to study current-induced atomic dynamics in a partially dehydrogenated armchair graphene nanoribbon. All parameters are obtained from density functional theory. The dehydrogenated carbon dimers behave as effective impurities, whose motion decouples from the rest of carbon atoms. The electrical current can couple the dimer motion in a coherent fashion. The coupling, which is mediated by nonconservative and pseudo-magnetic current-induced forces, change the atomic dynamics, and thereby show their signature in this simple system. We study the atomic dynamics and current-induced vibrational instabilities using a simplified eigen-mode analysis. Our study illustrates how armchair nanoribbons can serve as a possible testbed for probing the current-induced forces.

scholarly journals Controlling Multiple Orderings in Metal Thiocyanate Molecular Perovskites Ax{Ni[Bi(SCN)6]}

2020 ◽  
Author(s):  
Jie Yie Lee ◽  
Sanliang Ling ◽  
Stephen Argent ◽  
Mark Senn ◽  
Laura Cañadillas-Delgado ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Double Perovskites ◽  
Functional Theory ◽  
X Ray ◽  
Vacancy Ordering ◽  
A Site ◽  
Symmetry Mode ◽  
Site Vacancy

<p>We report four new A-site vacancy ordered thiocyanate double double perovskites,</p><p>A1􀀀xfNi[Bi(SCN)6]1􀀀x3 }, A = K<sup>+</sup>, NH4<sup>+</sup>, CH3(NH3)<sup>+</sup> (MeNH<sub>3</sub><sup>+</sup>) and C(NH<sub>2</sub>)<sub>3</sub><sup>+</sup> (Gua<sup>+</sup>), including the first examples of thiocyanate perovskites containing organic A-site cations. We show, using a combination of X-ray and neutron diffraction, that the structure of these frameworks depends on the A-site cation, and that these frameworks possess complex vacancy-ordering patterns and cooperative octahedral tilts distinctly different from atomic perovskites. Density functional theory calculations uncover the energetic origin of these complex orders and allow us to propose a simple rule to predict favoured A-site cation orderings for a given tilt sequence. We use these insights, in combination with symmetry mode analyses, to show that these complex orders offer a new route to non-centrosymmetric perovskites which render them as excellent candidates for</p><p>piezo- and ferroelectric applications.</p>

scholarly journals Controlling Multiple Orderings in Metal Thiocyanate Molecular Perovskites Ax{Ni[Bi(SCN)6]}

2020 ◽  
Author(s):  
Jie Yie Lee ◽  
Sanliang Ling ◽  
Stephen Argent ◽  
Mark Senn ◽  
Laura Cañadillas-Delgado ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Double Perovskites ◽  
Functional Theory ◽  
X Ray ◽  
Vacancy Ordering ◽  
A Site ◽  
Symmetry Mode ◽  
Site Vacancy

<p>We report four new A-site vacancy ordered thiocyanate double double perovskites,</p><p>A1􀀀xfNi[Bi(SCN)6]1􀀀x3 }, A = K<sup>+</sup>, NH4<sup>+</sup>, CH3(NH3)<sup>+</sup> (MeNH<sub>3</sub><sup>+</sup>) and C(NH<sub>2</sub>)<sub>3</sub><sup>+</sup> (Gua<sup>+</sup>), including the first examples of thiocyanate perovskites containing organic A-site cations. We show, using a combination of X-ray and neutron diffraction, that the structure of these frameworks depends on the A-site cation, and that these frameworks possess complex vacancy-ordering patterns and cooperative octahedral tilts distinctly different from atomic perovskites. Density functional theory calculations uncover the energetic origin of these complex orders and allow us to propose a simple rule to predict favoured A-site cation orderings for a given tilt sequence. We use these insights, in combination with symmetry mode analyses, to show that these complex orders offer a new route to non-centrosymmetric perovskites which render them as excellent candidates for</p><p>piezo- and ferroelectric applications.</p>

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