Анализ вычислительных и экспериментальных исследований переключения поляризации в ПВДФ и П (ВДФ-ТрФЭ) сегнетоэлектрических пленках на наноуровне

2015 ◽  
Vol 10 (2) ◽  
pp. 372-386 ◽  
Author(s):  
В.С. Быстров ◽  
V.S. Bystrov
Keyword(s):  
Experimental Data ◽  
Molecular Dynamics ◽  
Electric Field ◽  
Quantum Chemical ◽  
Polyvinylidene Fluoride ◽  
Domain Switching ◽  
Polarization Switching ◽  
Molecular Structures ◽  
Switching Mechanism ◽  
Semi Empirical

In this paper, molecular models are used to investigate and analyze the polarization switching in the polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) Langmuir-Blodgett (LB) nanofilms, in comparison with the experimental data at the nanoscale. Quantum-mechanical calculations and modeling, as well as molecular dynamics (MD) simulations based on semi-empirical quantum-chemical methods (such as PM3), show that the energy of the studied PVDF and P (VDF-TrFE) molecular structures, and their polarization switching proceed by the intrinsic homogeneous switching mechanism in the framework of the phenomenological theory of Landau-Ginzburg-Devonshire (LGD) in the linear approximation at low values of the electric field. The magnitude of the resulting critical coercive field is within the EC ~ 0.5 ... 2.5 GV/m, which is consistent with experimental data. It is also found that the uniform polarization switching mechanism of the polymer chains PVDF and P (VDF-TrFE) is due to the quantum properties of the molecular orbitals of the electron subsystem. This is clearly seen in both the polarization hysteresis loops, and the total energy changes. In this case, the turnover chain time, obtained by molecular dynamics within semi-empirical quantum-chemical PM3 approach in a limited Hartree-Fock approximation, when approaching this critical point, increases sharply, tending to infinity, which corresponds to the theory of LGD. Otherwise, at the high values of the applied electric field the polarization switching correspond to the extrinsic domain mechanism in the frame of the microscopic Kolmogorov–Avrami–Ishibashi (KAI) theory, describing bulk ferroelectric crystals and thick films. The performed analysis of computational and experimental data allows us to estimate the critical sizes of the possible transition region approximately on the order of 10 nm between intrinsic homogeneous and extrinsic domain switching mechanisms.

Computer modeling and molecular dynamics of polarization switching in the ferroelectric films PVDF and P(VDF-TrFE) on nanoscale

2015 ◽  
Vol 10 (1) ◽  
pp. 131-153 ◽  
Author(s):  
В.Е. Геворкян ◽  
V.E. Gevorkyan
Keyword(s):  
Molecular Dynamics ◽  
Electric Field ◽  
Total Energy ◽  
Critical Point ◽  
Quantum Chemical ◽  
Polarization Switching ◽  
Total System ◽  
Switching Mechanism ◽  
Gradual Shift ◽  
Semi Empirical

In this paper, molecular models are used to investigate and analyze the structure and polarization of polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) Langmuir-Blodgett (LB) nanofilms, depending on the structure and composition of the monomers of their polymer and copolymer chains. Quantum-mechanical calculations and modeling, as well as molecular dynamics (MD) simulations based on semi-empirical quantum-chemical methods (such as PM3), show that the energy of the studied PVDF and P (VDF-TrFE) molecular structures, and their polarization switching proceed by homogeneous switching mechanism in the framework of the phenomenological theory of Landau-Ginzburg-Devonshire (LGD) in the linear approximation of low values of the electric field. The magnitude of the resulting critical coercive field is within the EC ~ 0.5 ... 2.0 GV/m, which is consistent with experimental data. It is also found that the uniform polarization switching mechanism of the polymer chains PVDF and P (VDF-TrFE) is due to the quantum properties of the molecular orbitals of the electron subsystem: the applied electric field induces a gradual shift of the electron "clouds" density (electron polarizability), which in turn causes a gradual shift of the nuclear cores, in accordance with the principle of minimum total energy of the system, and this leads eventually, when it reaches a critical point (bifurcation) - to overturn of the entire chain and a sharp decrease in the total energy of the total system to its energetically more favorable state. This is clearly seen in both the polarization hysteresis loops, and the total energy changes. In this case, the turnover chain time, obtained by molecular dynamics within semi-empirical quantum-chemical PM3 approach in a limited Hartree-Fock approximation, when approaching this critical point, increases sharply, tending to infinity, which corresponds to the theory of LGD.

Loading Rate Effect on the Domain Switching of Ferroelectric Materials

2008 ◽  
Author(s):  
Ajit Achuthan ◽  
Chin-Teh Sun
Keyword(s):  
Electric Field ◽  
Loading Rate ◽  
Domain Switching ◽  
Underlying Mechanism ◽  
Ferroelectric Materials ◽  
Switching Behavior ◽  
Switching Mechanism ◽  
Two Factors ◽  
Different Characteristics ◽  
Butterfly Behavior

A method to characterize the strain electric field butterfly behavior based on the underlying domain switching mechanism is presented at first. The effect of loading rate on the different characteristics of the strain electric-field-butterfly behavior is then studied. By comparing the changes in these characteristics under different loading rates, it is established that the loading rate dependence of the strain electric field butterfly behavior is mainly due to two factors, 1) the dependence of the switching of individual domains on the magnitude and duration of the loading time and 2) the variation of the transition electric field with the loading rate. Several interesting attributes of the domain switching behavior that may shed light on understanding the underlying mechanism of domain switching further is illustrated in the present study. The present study also demonstrates that the method of characterizing the strain electric butterfly based on the underlying domain switching mechanism is very effective in studying ferroelectric behavior under different loading conditions.

scholarly journals Quantum chemical approach to calculating the enthalpies of the formation of alkali metal xanthates

2020 ◽  
Vol 15 (2) ◽  
pp. 30-37
Author(s):  
Yu. V. Popov ◽  
A. S. Dolgachev ◽  
E. V. Shishkin ◽  
Yu. L. Zotov ◽  
V. E. Shishkin
Keyword(s):  
Experimental Data ◽  
Alkali Metal ◽  
Quantum Chemical ◽  
Linear Regression Analysis ◽  
Biologically Active ◽  
Enthalpies Of Formation ◽  
Regression Equations ◽  
Flotation Reagents ◽  
Organic Part ◽  
Semi Empirical

Objectives. The aim of this work is to study the possibility of the joint use of quantum chemical methods and correlation analysis to determine the formation enthalpies of metal-containing organic substances using the example of alkali metal xanthates, which are of interest as biologically active substances and effective flotation reagents. Methods. Semi-empirical methods of quantum chemical calculating (Modified Neglect of Diatomic Overlap, Austin Model 1, Recife model 1 methods) and linear regression analysis were used. Results. Using the semi-empirical Modified Neglect of Diatomic Overlap, Austin Model 1, and Recife model 1 methods, the enthalpies of formation of 16 potassium and sodium alkyl xanthates were calculated, and the obtained results were compared with experimental data. It was found that the best correlation for potassium and sodium salts of dithiocarbonic acid esters could be observed using the Austin Model 1 method. Using the obtained regression equations, the enthalpies of formation were calculated for 30 xanthates, the organic part of which contained alkyl, cyclic non-aromatic structures, and one or two heteroatoms such as nitrogen, oxygen, and fluorine, and for which there are no experimental data. Conclusions. As a result of the study, an excellent correlation was established between the experimental and the calculated (by the Austin Model 1 method) values of the enthalpies of formation of potassium and sodium alkyl xanthates. The data obtained can be used to calculate the thermal effect of the xanthogenation reactions of alcohols and to design the production of the corresponding xanthates. 

scholarly journals Shear-strain-mediated large nonvolatile tuning of ferromagnetic resonance by an electric field in multiferroic heterostructures

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Ming Zheng ◽  
Takamasa Usami ◽  
Tomoyasu Taniyama
Keyword(s):  
Electric Field ◽  
Shear Strain ◽  
Ferromagnetic Resonance ◽  
Domain Switching ◽  
Coupling Effect ◽  
Resonance Field ◽  
Polarization Switching ◽  
Information Storage ◽  
Strain Effect ◽  
Multiferroic Heterostructures

AbstractControlling magnetism by an electric field is of critical importance for the future development of ultralow-power electronic and spintronic devices. Progress has been made in electrically driven nonvolatile tuning of magnetic states in multiferroic heterostructures for the information storage industry, which is exclusively attributed to the ferroelectric-polarization-switching-induced interfacial charge effect or nonlinear lattice strain effect. Here, we demonstrate that a hitherto unappreciated shear strain in the ferroelectric 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 substrate triggered by an electric field can be adopted to obtain robust nonvolatile control of the ferromagnetic resonance in an elastically coupled epitaxial Fe70Rh30 thin film. The disappearance of the resonance peak in a low-field-sweeping mode and the large resonance field shift of 111 Oe upon polarization switching demonstrate a strong shear-strain-mediated magnetoelectric coupling effect. In particular, in situ Kerr measurement identifies that the nonvolatile magnetic switching purely originates from electric-field-induced 109° ferroelastic domain switching rather than from 71°/180° ferroelectric domain switching even without the assistance of a magnetic field. This discovery illustrates the role of shear strain in achieving electrically tunable nonvolatile modulation of dynamic magnetic properties, and favors the design of future energy-efficient magnetoelectric microwave devices.

scholarly journals Theoretical Simulation of the Zeke Spectra of Naphthalene From Single Vibronic Levels of S1

1999 ◽  
Vol 19 (1-4) ◽  
pp. 105-108 ◽  
Author(s):  
Fabrizia Negri ◽  
Marek Z. Zgierski
Keyword(s):  
Ab Initio ◽  
Quantum Chemical Calculations ◽  
Ground State ◽  
Quantum Chemical ◽  
Electronic States ◽  
Perturbative Expansion ◽  
Molecular Structures ◽  
Theoretical Simulation ◽  
Vibronic States ◽  
Semi Empirical

We present the simulations and analysis of the two-color ZEKE spectra of naphthalene, performed with the help of quantum chemical calculations of molecular parameters followed by the modelling of vibronic intensities. Ab initio and semi-empirical calculations were carried out to obtain molecular structures of neutral and ionic naphthalene, and vibronic perturbations that couple the electronic states. It is shown that the intensities, simulated with a model based on the perturbative expansion of vibronic states, nicely reproduce the observed spectra and contribute to reassign some of the ground state frequencies of naphthalene cation.

Study of the behavior of polyvinylidene fluoride (PVDF) under the action of electric field using semi-empirical methods (PM3)

2012 ◽  
pp. 1544-1546
Author(s):  
Elson C. Santos ◽  
Rafael M. E. Santo ◽  
Danilo C. Pedrelli ◽  
Julio C.N. Aires ◽  
Teodorico C. Ramalho ◽  
...  
Keyword(s):  
Electric Field ◽  
Polyvinylidene Fluoride ◽  
Empirical Methods ◽  
Semi Empirical

scholarly journals Applying joint theoretical experimental research to aptamer modeling

2021 ◽  
pp. 105-106
Author(s):  
I.A. Shchugoreva ◽  
◽  
P.V. Artyushenko ◽  
F.N. Tomilin ◽  
D.I. Morozov ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Quantum Chemical ◽  
Density Functional ◽  
3D Structure ◽  
Tight Binding ◽  
Molecular Simulations ◽  
Molecular Structures ◽  
Dna Aptamer ◽  
Dynamic Simulations ◽  
Theoretical Methods

The aim of the research. In this work we studied the structure of LC-18 DNA aptamer, which exhibits specifi c binding to lung adenocarcinoma cells. Obtaining the 3D structure of the aptamer is necessary for understanding the mechanism of binding of the aptamer to the target. Th erefore, the aim of the research was modeling of the LC-18 aptamer spatial structure using combination of theoretical methods: DNA folding tools, quantum-chemical calculations and molecular dynamic simulations. Material and methods. Th e secondary structure of the LC-18 aptamer was predicted by using OligoAnalyzer and MFold online soft ware under the conditions typical small-angle X-ray scattering (SAXS) experiment. Th e molecular modeling of the aptamer was carried out using the Avogadro program. For prediction of the structure two computational methods were used: quantum-mechanical method with third-order density-functional tight-binding (DFTB3) and molecular dynamics (MD) with force fi elds. Results. In this paper it was shown that molecular simulations can predict structures from the SAXS experiments. OligoAnalyzer and MFold web servers have been used to generate a set of several likely models. However, more accurate calculations have showed that these models do not predict the relative importance of isomers. Meanwhile, application of quantum-chemical and molecular dynamics calculations have showed reliable molecular structures which have a small deviations from the experimental SAXS curves. Conclusion. Th is study demonstrates the approach for modeling 3D structures of DNA-aptamers in solution using both experimental and theoretical methods. It could be very helpful in designing more effi cient aptamers based on results obtained from molecular simulations.

Electric field control of proton-transfer molecular switching: molecular dynamics study on salicylidene aniline

2015 ◽  
Vol 17 (22) ◽  
pp. 14484-14488 ◽  
Author(s):  
Joanna Jankowska ◽  
Joanna Sadlej ◽  
Andrzej L. Sobolewski
Keyword(s):  
Molecular Dynamics ◽  
Electric Field ◽  
Proton Transfer ◽  
Intramolecular Proton Transfer ◽  
Molecular Switch ◽  
Molecular Switching ◽  
Switching Mechanism ◽  
Field Control

In this letter, we propose a novel, ultrafast, efficient molecular switch whose switching mechanism involves the electric field-driven intramolecular proton transfer.

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