scholarly journals TERAHERTZ DIELECTRIC RESPONSE AND COUPLED DYNAMICS OF FERROELECTRICS AND MULTIFERROICS FROM EFFECTIVE HAMILTONIAN SIMULATIONS

2013 ◽  
Vol 27 (22) ◽  
pp. 1330016 ◽  
Author(s):  
DAWEI WANG ◽  
JEEVAKA WEERASINGHE ◽  
ABDULLAH ALBARAKATI ◽  
L. BELLAICHE
Keyword(s):  
First Principles ◽  
Md Simulation ◽  
Functional Materials ◽  
Simulation Method ◽  
Effective Hamiltonian ◽  
Multiferroic Materials ◽  
Future Directions ◽  
Technical Details ◽  
Complex Phenomena ◽  
Effective Hamiltonians

Ferroelectric and multiferroic materials form an important class of functional materials. Over the last 20 years, first-principles-based effective Hamiltonian approaches have been successfully developed to simulate these materials. In recent years, effective Hamiltonian approaches were combined with molecular dynamics (MD) methods to investigate terahertz dynamical properties of various perovskites. With this combination, a variety of ferroelectric and multiferroic materials, including BaTiO 3, Ba(Sr, Ti)O 3, Pb(Zr, Ti)O 3, BiFeO 3 and SrTiO 3 bulks and films have been simulated, which led to the understanding of complex phenomena and discovery of novel effects. In this paper we first provide technical details about effective Hamiltonians and MD simulation method. Then, we present applications of the combination of these two techniques to different perovskites. Finally, we briefly discuss possible future directions of this approach.

Influence of Flexible Side-Chains on the Breathing Phase Transition of Pillared Layer MOFs: A Force Field Investigation

2020 ◽  
Author(s):  
Julian Keupp ◽  
Johannes P. Dürholt ◽  
Rochus Schmid
Keyword(s):  
First Principles ◽  
Good Accuracy ◽  
Field Investigation ◽  
Square Lattice ◽  
Side Chain ◽  
Second Step ◽  
Side Chains ◽  
Dynamics Simulations ◽  
Complex Phenomena ◽  
Closed Pore

The prototypical pillared layer MOFs, formed by a square lattice of paddle-<br>wheel units and connected by dinitrogen pillars, can undergo a breathing phase<br>transition by a “wine-rack” type motion of the square lattice. We studied this not<br>yet fully understood behavior using an accurate first principles parameterized force<br>field (MOF-FF) for larger nanocrystallites on the example of Zn 2 (bdc) 2 (dabco) [bdc:<br>benzenedicarboxylate, dabco: (1,4-diazabicyclo[2.2.2]octane)] and found clear indi-<br>cations for an interface between a closed and an open pore phase traveling through<br>the system during the phase transformation [Adv. Theory Simul. 2019, 2, 11]. In<br>conventional simulations in small supercells this mechanism is prevented by periodic<br>boundary conditions (PBC), enforcing a synchronous transformation of the entire<br>crystal. Here, we extend this investigation to pillared layer MOFs with flexible<br>side-chains, attached to the linker. Such functionalized (fu-)MOFs are experimen-<br>tally known to have different properties with the side-chains acting as fixed guest<br>molecules. First, in order to extend the parameterization for such flexible groups,<br>1a new parametrization strategy for MOF-FF had to be developed, using a multi-<br>structure force based fit method. The resulting parametrization for a library of<br>fu-MOFs is then validated with respect to a set of reference systems and shows very<br>good accuracy. In the second step, a series of fu-MOFs with increasing side-chain<br>length is studied with respect to the influence of the side-chains on the breathing<br>behavior. For small supercells in PBC a systematic trend of the closed pore volume<br>with the chain length is observed. However, for a nanocrystallite model a distinct<br>interface between a closed and an open pore phase is visible only for the short chain<br>length, whereas for longer chains the interface broadens and a nearly concerted trans-<br>formation is observed. Only by molecular dynamics simulations using accurate force<br>fields such complex phenomena can be studied on a molecular level.

scholarly journals A Ternary Map of Ni–Mn–Ga Heusler Alloys from Ab Initio Calculations

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 973
Author(s):  
Yulia Sokolovskaya ◽  
Olga Miroshkina ◽  
Danil Baigutlin ◽  
Vladimir Sokolovskiy ◽  
Mikhail Zagrebin ◽  
...  
Keyword(s):  
First Principles ◽  
Predictive Power ◽  
Computational Study ◽  
Heusler Alloys ◽  
Functional Materials ◽  
Ternary Diagram ◽  
Compositional Stability ◽  
Theoretical Predictions ◽  
Simultaneous Stability ◽  
Tetragonal Martensite

In the search for new magnetic functional materials, non-stoichiometric compounds remain a relatively unexplored territory. While experimentalists create new compositions looking for improved functional properties, their work is not guided by systematic theoretical predictions. Being designed for perfect periodic crystals, the majority of first-principles approaches struggle with the concept of a non-stoichiometric system. In this work, we attempt a systematic computational study of magnetic and structural properties of Ni–Mn–Ga, mapped onto ternary composition diagrams. Compositional stability was examined using the convex hull analysis. We show that the cubic austenite has its stability region close to the stoichiometric Ni2MnGa, in agreement with experimental data, while the tetragonal martensite spreads its stability over a wider range of Mn and Ni contents. The unstable compositions in both austenite and martensite states are located in the Ga-rich corner of the ternary diagram. We note that simultaneous stability of the austenite and martensite should be considered for potentially stable compounds suitable for synthesis. The majority of compounds are predicted to be ferrimagnetically ordered in both austenitic and martensitic states. The methodology used in this work is computationally tractable, yet it delivers some predictive power. For experimentalists who plan to synthesize stable Ni–Mn–Ga compounds with ferromagnetic order, we narrow the target compositional range substantially.

scholarly journals First-Principles Atomistic Thermodynamics and Configurational Entropy

2020 ◽  
Vol 8 ◽  
Author(s):  
Christopher Sutton ◽  
Sergey V. Levchenko
Keyword(s):  
First Principles ◽  
Configurational Entropy ◽  
Functional Materials ◽  
Expansion Method ◽  
Bulk Materials ◽  
Cluster Expansion Method ◽  
Particle Exchange ◽  
Properties Of Materials ◽  
Atomistic Thermodynamics ◽  
Statistical Effects

In most applications, functional materials operate at finite temperatures and are in contact with a reservoir of atoms or molecules (gas, liquid, or solid). In order to understand the properties of materials at realistic conditions, statistical effects associated with configurational sampling and particle exchange at finite temperatures must consequently be taken into account. In this contribution, we discuss the main concepts behind equilibrium statistical mechanics. We demonstrate how these concepts can be used to predict the behavior of materials at realistic temperatures and pressures within the framework of atomistic thermodynamics. We also introduce and discuss methods for calculating phase diagrams of bulk materials and surfaces as well as point defect concentrations. In particular, we describe approaches for calculating the configurational density of states, which requires the evaluation of the energies of a large number of configurations. The cluster expansion method is therefore also discussed as a numerically efficient approach for evaluating these energies.

scholarly journals Nanotechnology: A Journey towards Finding Solutions

2015 ◽  
Vol 5 (1) ◽  
pp. 61
Author(s):  
Satya Pal Singh
Keyword(s):  
Health And Safety ◽  
Functional Materials ◽  
Simulation Method ◽  
Industrial Applications ◽  
Policy Makers ◽  
Advance Research ◽  
American Physical ◽  
Richard Feynman ◽  
And Control ◽  
Thin Film Magnetism

<p class="1Body">Nanotechnology is the understanding and control of matter at the diemnsions ranging between 1-100 nm. One nanometer is one billionth of a meter. Nanotechnology involves manipulation of atoms, imaging, measuring and modelling at nano scale. Its potentials were first highlighted by Richard Feynman in the American Physical Scociety meeting in 1959. Though, he did not coin the world nanotechnology himself but he explored the possiblities of functional materials at the bottom of the scale. In last two decades this technology has been commercialized to great extent and gaining importance day by day influencing the economies of different countries and henceforth enforcing the policy makers to address the issues like environment, health and safety. Governments are regularisaing and monitoring its research, uses, applications and technology transfer which includes intelluctaul property rights. This paper addresses the dimensions and trends of nanotechnology covering economic aspects. The paper is focussed on the changes in the functional properties of nanomaterials as physical, chemical, optical, electronic, electrical, magnetic etc. in comparision to those of the bulk of material. It has been discussed how the basic and advance research in nanoscience could be explotiedfor making technologies for its commercial and industrial applications for the benefit and safety of the soceity. Thin film magnetism is demonstrated using Monte Carlo simulation method. Experimental synthesisof some of thenanorods and qunatum dots are also discussed.</p>

scholarly journals Effective Hamiltonians and Wavefunctions for Electrons in Deformed Crystals

1983 ◽  
Vol 36 (3) ◽  
pp. 321 ◽  
Author(s):  
RA Brown
Keyword(s):  
Hilbert Space ◽  
Probability Density ◽  
Physical Interpretation ◽  
Wannier Function ◽  
Deformation Potential ◽  
Effective Hamiltonian ◽  
Wannier Functions ◽  
Modulating Functions ◽  
Strain Dependent ◽  
Effective Hamiltonians

An effective Hamiltonian for electrons in in homogeneously deformed crystals is derived by expanding the wavefunction in terms of Wannier functions of the homogeneously deformed crystal. The physical interpretation of the modulating functions which determine the amplitude of each Wannier function in the expansion, and which are governed by the effective Hamiltonian, is investigated. This leads to strain-dependent expressions for the probability density and current, averaged over the fluctuations within each unit cell. The operators which represent, in the Hilbert space of the . modulating functions, similarly averaged physical observables are introduced and explicit straindependent expressions for the velocity and momentum operators are obtained. Applications of the theory are foreshadowed and its relationship to previous deformation-potential theories is examined.

scholarly journals Understanding the interaction properties of an eco-friendly corrosion inhibitor on Zn (1 1 0) surface: Comprehensive DFT-based MD simulation

2021 ◽  
Author(s):  
Atyeh Rahmanzadeh ◽  
Mahyar Rezvani ◽  
Masoud Darvish Ganji
Keyword(s):  
Interaction Energy ◽  
Active Sites ◽  
Md Simulation ◽  
Functional Materials ◽  
Metallic Surfaces ◽  
Theory Analysis ◽  
Multiple Bonds ◽  
Green Inhibitor ◽  
Wide Range ◽  
Interactive Nature

Abstract Regarding the deleterious effects of corrosion for a wide range of metals and alloys, many different techniques have been developed to protect the metals against corrosion. Utilizing organic inhibitors, especially those that contain heteroatoms and multiple bonds has been found an effective approach. In this research, the adsorption of a novel green inhibitor, Laurhydrazide N′-propan-3-one (LHP), on the Zn (110) surface was investigated using dispersion corrected DFT calculations. Interaction energy and electronic structures were calculated for different orientations of the inhibitor toward the Zn surface. The validity of calculated interaction energy has been verified by the MP2 level of theory. The AIM theory analysis revealed that LHP bound strongly to the Zn surface through its O active site and also its orientation affects greatly the interaction energy. Furthermore, diffusion of LHP through its O atoms active sites was observed with the state-of-the-art DFT-MD simulation during the simulation procedure that agrees well with the experiments for similar molecules adsorbed on the metal surfaces. The presented findings afford a vital insight into the interactive nature of adsorbed inhibitors on metallic surfaces and will help to develop advanced functional materials in coating technologies.

W(h)ither Media Influence?

2000 ◽  
Vol 95 (1) ◽  
pp. 19-27 ◽  
Author(s):  
Stuart Cunningham ◽  
Angela Romano
Keyword(s):  
New Media ◽  
First Principles ◽  
Media Influence ◽  
Complex Flows ◽  
Future Directions ◽  
Policy Makers ◽  
Media Regulation ◽  
Policy Domain ◽  
The Subject ◽  
Central Term

During 1999–2000, the Productivity Commission's inquiry into Broadcasting, together with the ABA's ‘cash for comment’ inquiry, painted the old shibboleth of media influence in a new light. Influence has been a central term in government media regulation, but the term has rarely been interrogated from first principles in the policy domain. Assumptions have been made about the greater influence of television compared with radio, in spite of ongoing controversy centring around the cash for comment inquiry that has spotlighted both the power of talkback radio kings and their potential to misuse it. Policy-makers and politicians have also been overly optimistic about the potential of new media forms to ameliorate concentration of influence in the hands of media oligopolies. After examining the complex flows of influence within and between media organisations, this paper lists several recommendations for future directions in research on the subject.

scholarly journals Molecular dynamic simulation of CO2 absorption into mixed aqueous solutions MDEA/PZ

2017 ◽  
Vol 19 ◽  
pp. 1 ◽  
Author(s):  
Noorlisa Harun ◽  
Emyra Ezzaty Masiren
Keyword(s):  
Intermolecular Interaction ◽  
Md Simulation ◽  
Chemical Engineering ◽  
Time Integration ◽  
Simulation Method ◽  
Hydroxyl Group ◽  
Co2 Absorption ◽  
Engineering Research ◽  
Heat Regeneration ◽  
Amine Absorption

<p>The mixture of amine absorption process is an approach for mitigation of carbon dioxide (CO<sub>2</sub>) from flue gas that produces from power plant. Several experimental and simulation studies have been undertaken to understand this process but the mechanism of CO<sub>2</sub> absorption into the aqueous blended amines such as MDEA/PZ is not well understood and available knowledge within the open literature is limited. The aim of this study is to investigate the intermolecular interaction of the blended MDEA/PZ using Molecular Dynamics (MD) simulation. MD simulation was run under condition 313 K and 1 atm. The thermodynamic ensemble used were 200 ps for NVE and 1 ns for NVT. The periodic boundary is used to visualize the interaction of molecules of the whole system. The simulation method also involved calculation of force field and time integration algorithm.The results were interpreted in terms of Radial Distribution Function (RDF) analysis. It was observed that the hydroxyl group (–OH) of MDEA is more attracted to water molecule compared to amino group (–NH) of MDEA. The intermolecular interaction probability of –OH and –NH group of MDEA with CO<sub>2</sub> in blended MDEA/PZ is higher than using pure MDEA. This finding shows that PZ molecule act as an activator to promote the intermolecular interaction between MDEA and CO<sub>2</sub>.Thus, blend of MDEA with PZ is expecting to increase the absorption rate of CO2 and reduce the heat regeneration requirement.</p><p>Chemical Engineering Research Bulletin 19(2017) 1-11</p>

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