First-Principles Calculations and Molecular Dynamics Simulations on Effect of Hydrogen Impurity in Lead Titanate Films

2016 ◽  
Author(s):  
Lin Zhu ◽  
Jeong Ho You ◽  
Jinghong Chen
Keyword(s):  
Molecular Dynamics ◽  
First Principles ◽  
Hysteresis Loops ◽  
Md Simulations ◽  
Energy Difference ◽  
Effective Hamiltonian ◽  
First Principles Calculations ◽  
Hydrogen Impurity ◽  
Penalty Term ◽  
Energy Penalty

Properties of ferroelectric films are highly influenced by inevitable defects, such as hydrogen impurity. This study is focused on theoretical and numerical studies to probe effects of hydrogen contamination on ferroelectric stability in PbTiO3 (PTO) films using the first-principles effective Hamiltonian. First-principles calculations are performed to determine the possible position, formation energy, and mobility of hydrogen impurity atom, and the calculated results are used as inputs to molecular dynamics (MD) simulations in a large system. The hydrogen atom is able to move along the polarization with small energy barriers. The energy difference between a hydrogen contaminated PTO and a pure PTO is considered as an energy penalty term induced by hydrogen contamination and has been added to the effective Hamiltonian. Then, the MD effective Hamiltonian with the energy penalty is employed in MD simulations to investigate the effects of hydrogen contamination on the ferroelectric responses of PTO films with various thicknesses and temperatures. The hysteresis loops are presented and analyzed for PTO films with various concentrations of hydrogen impurities and thicknesses. Hydrogen contamination reduces the remnant polarization, especially for thin films. As the concentration of hydrogen impurities increases, the critical thickness increases. By analyzing the vertical cross section snapshots, it has been found that the hydrogen impurity atoms near interfaces affect the polarization throughout the entire PTO films.

Theoretical studies of structural stability at high pressure

1995 ◽  
Vol 73 (5-6) ◽  
pp. 253-257 ◽  
Author(s):  
John S. Tse ◽  
Dennis D. Klug
Keyword(s):  
Molecular Dynamics ◽  
High Pressure ◽  
First Principles ◽  
High Pressures ◽  
Structural Phase ◽  
Md Simulations ◽  
Quantum Molecular Dynamics ◽  
First Principles Calculations ◽  
Quantum Mechanical Effects ◽  
Structural Memory

Theoretical methods are indispensible for the study of matter at high pressure. In the last decade the development of accurate intermolecular potentials and the methodologies in classical molecular dynamics (MD) simulations have greatly facililated the applications of these methods to the study of structural phase transformamtions of solids at high pressures. More recently, it has been possible to incorporate quantum mechanical effects into MD calculations. This method eliminates a great deal of empiricism. These first principles calculations have not only reproduced the experimental results for phase transformations but also provided detailed mechanisms and in some cases predicted new structures that may be found at high pressures. The success of MD calculations is illustrated through a review of our studies of pressure-induced amorphization and phase transitions in SiO2 and TiO2, and the structural memory effect in several materials. Current applications using quantum molecular dynamics on ice are discussed.

Atomic simulations of GB sliding in pure and segregated bicrystals

2013 ◽  
Vol 1515 ◽  
Author(s):  
Motohiro Yuasa ◽  
Yasumasa Chino ◽  
Mamoru Mabuchi
Keyword(s):  
Molecular Dynamics ◽  
Electronic Structure ◽  
Grain Boundary ◽  
Charge Density ◽  
First Principles ◽  
Deformation Mode ◽  
Md Simulations ◽  
Bond Critical Point ◽  
First Principles Calculations ◽  
Atomic Simulations

ABSTRACTGrain boundary (GB) sliding is an important deformation mode in polycrystals, and it has been extensively investigated, for example, there are many studies on influences of the atomic geometry in the GB region. However, it is important to investigate GB sliding from the electronic structure of GB for deeper understandings of the sliding mechanisms. In the present work, we investigated the GBs sliding in pure and segregated bicrystals with classical molecular dynamics (MD) simulations and first-principles calculations. It is accepted that the sliding rate is affected by the GB energy. However, there was no correlation between the sliding rate and the GB energy in either the pure or the segregated bicrystals. First-principles calculations revealed that the sliding rate calculated by the MD simulations increases with decreasing minimum charge density at the bond critical point in the GB. This held in both the pure and segregated bicrystals. It seems that the sliding rate depends on atomic movement at the minimum charge density sites.

Discrete breathers modeling from first principles in graphene and in classical approximation in fcc Ni: Comparison

2019 ◽  
Vol 04 (02) ◽  
pp. 1950002 ◽  
Author(s):  
Ivan P. Lobzenko
Keyword(s):  
Molecular Dynamics ◽  
First Principles ◽  
High Frequency ◽  
Normal Modes ◽  
Nonlinear Normal Modes ◽  
First Principles Calculations ◽  
Discrete Breathers ◽  
Points Of View ◽  
Nonlinear Normal ◽  
Dynamics Simulations

Properties of discrete breathers are discussed from two points of view: (I) the ab initio modeling in graphene and (II) classical molecular dynamics simulations in the ace-centered cubic (fcc) Ni. In the first (I) approach, the possibility of exciting breathers depends on the strain applied to the graphene sheet. The uniaxial strain leads to opening the gap in the phonon band and, therefore, the existence of breathers with frequencies within the gap. In the second (II) approach, the structure of fcc Ni supports breathers of another kind, which possess a hard nonlinearity type. It is shown that particular high frequency normal mode can be used to construct the breather by means of overlaying a spherically symmetrical function, the maximum of which coincides with the breather core. The approach of breathers excitation based on nonlinear normal modes is independent of the level of approximation. Even though breathers could be obtained both in classical and first-principles calculations, each case has advantages and shortcomings, that are compared in the present work.

Na ion dynamics in P2-Nax[Ni1/3Ti2/3]O2: a combination of quasi-elastic neutron scattering and first-principles molecular dynamics study

2020 ◽  
Vol 8 (47) ◽  
pp. 25290-25297
Author(s):  
Qian Chen ◽  
Niina H. Jalarvo ◽  
Wei Lai
Keyword(s):  
Molecular Dynamics ◽  
Neutron Scattering ◽  
First Principles ◽  
Md Simulations ◽  
First Principle ◽  
Ion Dynamics ◽  
Elastic Neutron ◽  
Elastic Neutron Scattering ◽  
First Principles Molecular Dynamics

The Na dynamics in P2-Nax[Ni1/3Ti2/3]O2 were investigated through a combination of QENS experiments and first-principle MD simulations.

Molecular Dynamics Simulation of Bi-Carboxyl Sidewall Functionalized Single-Wall Carbon Nanotubes in Water

2015 ◽  
Vol 1131 ◽  
pp. 106-109
Author(s):  
Shongpun Lokavee ◽  
Chatchawal Wongchoosuk ◽  
Teerakiat Kerdcharoen
Keyword(s):  
Carbon Nanotubes ◽  
Molecular Dynamics ◽  
Md Simulations ◽  
Dynamics Simulation ◽  
Single Wall Carbon Nanotubes ◽  
First Principles Calculations ◽  
Carboxylic Groups ◽  
Potential Applications ◽  
Walled Carbon Nanotubes ◽  
Defective Sites

Functionalized single-walled carbon nanotubes (f-SWNTs) have attracted great interest due to their enhancement of SWNT properties leading to an increase in potential applications beyond those of pristine SWNT. In this work, we have investigated the behavior of open-end (9,0) bi-carboxyl sidewall functionalized SWNTs in water using molecular dynamics (MD) technique within GROMACS software package based on the OPLS force fields with modified charges obtained from the first principles calculations. The model tubes including perfect and defective nanotubes covalently functionalized by bi-carboxylic groups on different sidewall surface orientation were fully optimized by B3LYP/6-31G(d,p). The simulations were performed at the constant volume and temperature in a rectangular box with periodic boundary conditions in which each system contains one model tube and ~1680 water molecules. The results form MD simulations showed that functionalization on the central carbon atom in the (C1,C ́1)SW-defective sites strongly affects on the dynamic behavior of CNT in water. Results showed that the hydrophilic behavior of the functionalized SWNT has been improved over the pristine and defective nanotubes.

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