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.

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.

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.

Prediction of Alkanolamine pKa Values by Combined Molecular Dynamics Free Energy Simulations and ab initio Calculations

2019 ◽  
Author(s):  
Javad Noroozi ◽  
William Smith
Keyword(s):  
Molecular Dynamics ◽  
Free Energy ◽  
Ab Initio Calculations ◽  
Gas Phase ◽  
Quantum Chemical ◽  
Phase Reaction ◽  
Pka Values ◽  
Gas Phase Reaction ◽  
Reaction Free Energy ◽  
Energy Simulations

We use molecular dynamics free energy simulations in conjunction with quantum chemical calculations of gas phase reaction free energy to predict alkanolamines pka values. <br>

scholarly journals The Impact of the Electric Field on Surface Condensation of Water Vapor: Insight from Molecular Dynamics Simulation

Nanomaterials ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 64 ◽  
Author(s):  
Qin Wang ◽  
Hui Xie ◽  
Zhiming Hu ◽  
Chao Liu
Keyword(s):  
Molecular Dynamics ◽  
Water Vapor ◽  
Electric Field ◽  
Intermolecular Forces ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Attraction Force ◽  
Condensation Rate ◽  
Shape Transformation ◽  
The Impact

In this study, molecular dynamics simulations were carried out to study the coupling effect of electric field strength and surface wettability on the condensation process of water vapor. Our results show that an electric field can rotate water molecules upward and restrict condensation. Formed clusters are stretched to become columns above the threshold strength of the field, causing the condensation rate to drop quickly. The enhancement of surface attraction force boosts the rearrangement of water molecules adjacent to the surface and exaggerates the threshold value for shape transformation. In addition, the contact area between clusters and the surface increases with increasing amounts of surface attraction force, which raises the condensation efficiency. Thus, the condensation rate of water vapor on a surface under an electric field is determined by competition between intermolecular forces from the electric field and the surface.

scholarly journals An Investigation into the Approximations Used in Wave Packet Molecular Dynamics for the Study of Warm Dense Matter

Plasma ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 294-308
Author(s):  
William A. Angermeier ◽  
Thomas G. White
Keyword(s):  
Molecular Dynamics ◽  
Wave Packet ◽  
Hydrogen Plasma ◽  
Valence Bond ◽  
Dense Matter ◽  
Basis Set ◽  
Warm Dense Matter ◽  
Scaling Parameters ◽  
Oppenheimer Approximation ◽  
Semi Empirical

Wave packet molecular dynamics (WPMD) has recently received a lot of attention as a computationally fast tool with which to study dynamical processes in warm dense matter beyond the Born–Oppenheimer approximation. These techniques, typically, employ many approximations to achieve computational efficiency while implementing semi-empirical scaling parameters to retain accuracy. We investigated three of the main approximations ubiquitous to WPMD: a restricted basis set, approximations to exchange, and the lack of correlation. We examined each of these approximations in regard to atomic and molecular hydrogen in addition to a dense hydrogen plasma. We found that the biggest improvement to WPMD comes from combining a two-Gaussian basis with a semi-empirical correction based on the valence-bond wave function. A single parameter scales this correction to match experimental pressures of dense hydrogen. Ultimately, we found that semi-empirical scaling parameters are necessary to correct for the main approximations in WPMD. However, reducing the scaling parameters for more ab-initio terms gives more accurate results and displays the underlying physics more readily.

A memory nanodevice based on Zn-MOF-74: a molecular dynamics study

2020 ◽  
Vol 8 (5) ◽  
pp. 1567-1570 ◽  
Author(s):  
Mikhail Suyetin ◽  
Thomas Heine
Keyword(s):  
Molecular Dynamics ◽  
Electric Field ◽  
Memory Element ◽  
Switching Speed ◽  
High Switching Speed ◽  
Element Density

C60−@Zn-MOF-74 operated by an electric field exhibits a combined high switching speed of 27 GB s−1 and a high memory element density of 106 Tb per inch2.

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