Different Mechanisms of Translational Symmetry Breaking in Liquid-Crystal Coil–Rod–Coil Triblock Copolymers

A molecular-statistical theory of coil–rod–coil triblock copolymers with orientationally ordered rod-like fragments has been developed using the density functional approach. An explicit expression for the free energy has been obtained in terms of the direct correlation functions of the reference disordered phase, the Flory–Huggins parameter and the potential of anisotropic interaction between rigid rods. The theory has been used to derive several phase diagrams and to calculate numerically orientational and translational order parameter profiles for different polymer architecture as a function of the Flory–Huggins parameter, which specifies the short-range repulsion and as functions of temperature. In triblock copolymers, the nematic–lamellar transition is accompanied by the translational symmetry breaking, which can be caused by two different microscopic mechanisms. The first mechanism resembles a low dimensional crystallization and is typical for conventional smectic liquid crystals. The second mechanism is related to the repulsion between rod and coil segments and is typical for block copolymers. Both mechanisms are analyzed in detail as well as the effects of temperature, coil fraction and the triblock asymmetry on the transition into the lamellar phase.

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Liquid-Crystal Ordering and Microphase Separation in the Lamellar Phase of Rod-Coil-Rod Triblock Copolymers. Molecular Theory and Computer Simulations

Polymers ◽

10.3390/polym13193392 ◽

2021 ◽

Vol 13 (19) ◽

pp. 3392

Author(s):

Mikhail A. Osipov ◽

Maxim V. Gorkunov ◽

Alexander A. Antonov ◽

Anatoly V. Berezkin ◽

Yaroslav V. Kudryavtsev

Keyword(s):

Free Energy ◽

Correlation Functions ◽

Density Functional ◽

Diblock Copolymers ◽

Microphase Separation ◽

Triblock Copolymers ◽

Molecular Model ◽

Lamellar Phase ◽

Density Correlation ◽

Huggins Parameter

A molecular model of the orientationally ordered lamellar phase exhibited by asymmetric rod-coil-rod triblock copolymers has been developed using the density-functional approach and generalizing the molecular-statistical theory of rod-coil diblock copolymers. An approximate expression for the free energy of the lamellar phase has been obtained in terms of the direct correlation functions of the system, the Flory-Huggins parameter and the Maier-Saupe orientational interaction potential between rods. A detailed derivation of several rod-rod and rod-coil density-density correlation functions required to evaluate the free energy is presented. The orientational and translational order parameters of rod and coil segments depending on the temperature and triblock asymmetry have been calculated numerically by direct minimization of the free energy. Different structure and ordering of the lamellar phase at high and low values of the triblock asymmetry is revealed and analyzed in detail. Asymmetric rod-coil-rod triblock copolymers have been simulated using the method of dissipative particle dynamics in the broad range of the Flory-Huggins parameter and for several values of the triblock asymmetry. It has been found that the lamellar phase appears to be the most stable one at strong segregation. The density distribution of the coil segments and the segments of the two different rods have been determined for different values of the segregation strength. The simulations confirm the existence of a weakly ordered lamellar phase predicted by the density-functional theory, in which the short rods separate from the long ones and are characterized by weak positional ordering.

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More on the flavor dependence of mϱ/fπ

Journal of High Energy Physics ◽

10.1007/jhep07(2021)202 ◽

2021 ◽

Vol 2021 (7) ◽

Author(s):

Andrey Yu. Kotov ◽

Daniel Nogradi ◽

Kalman K. Szabo ◽

Lorinc Szikszai

Keyword(s):

Gauge Theory ◽

Symmetry Breaking ◽

Finite Volume ◽

Continuum Limit ◽

Low Energy ◽

Translational Symmetry ◽

Fundamental Representation ◽

Staggered Fermions ◽

Link Type ◽

Volume Effects

Abstract In previous work, [arXiv:1905.01909], we have calculated the mϱ/fπ ratio in the chiral and continuum limit for SU(3) gauge theory coupled to Nf = 2, 3, 4, 5, 6 fermions in the fundamental representation. The main result was that this ratio displays no statistically significant Nf-dependence. In the present work we continue the study of the Nf-dependence by extending the simulations to Nf = 7, 8, 9, 10. Along the way we also study in detail the Nf-dependence of finite volume effects on low energy observables and a particular translational symmetry breaking unphysical, lattice artefact phase specific to staggered fermions.

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Ab Initio Study of Ferroelectric Critical Size of SnTe Low-Dimensional Nanostructures

Nanomaterials ◽

10.3390/nano10040732 ◽

2020 ◽

Vol 10 (4) ◽

pp. 732 ◽

Cited By ~ 1

Author(s):

Takahiro Shimada ◽

Koichiro Minaguro ◽

Tao Xu ◽

Jie Wang ◽

Takayuki Kitamura

Keyword(s):

Density Functional ◽

Critical Size ◽

Density Functional Theory Calculations ◽

Cell Width ◽

Functional Theory ◽

Unit Cells ◽

Principle Density Functional Theory ◽

Low Dimensional ◽

Insight Into ◽

Ferroelectric Perovskite

Beyond a ferroelectric critical thickness of several nanometers existed in conventional ferroelectric perovskite oxides, ferroelectricity in ultimately thin dimensions was recently discovered in SnTe monolayers. This discovery suggests the possibility that SnTe can sustain ferroelectricity during further low-dimensional miniaturization. Here, we investigate a ferroelectric critical size of low-dimensional SnTe nanostructures such as nanoribbons (1D) and nanoflakes (0D) using first-principle density-functional theory calculations. We demonstrate that the smallest (one-unit-cell width) SnTe nanoribbon can sustain ferroelectricity and there is no ferroelectric critical size in the SnTe nanoribbons. On the other hand, the SnTe nanoflakes form a vortex of polarization and lose their toroidal ferroelectricity below the surface area of 4 × 4 unit cells (about 25 Å on one side). We also reveal the atomic and electronic mechanism of the absence or presence of critical size in SnTe low-dimensional nanostructures. Our result provides an insight into intrinsic ferroelectric critical size for low-dimensional chalcogenide layered materials.

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One-Fe versus Two-Fe Brillouin Zone of Fe-Based Superconductors: Creation of the Electron Pockets by Translational Symmetry Breaking

Physical Review Letters ◽

10.1103/physrevlett.107.257001 ◽

2011 ◽

Vol 107 (25) ◽

Cited By ~ 47

Author(s):

Chia-Hui Lin ◽

Tom Berlijn ◽

Limin Wang ◽

Chi-Cheng Lee ◽

Wei-Guo Yin ◽

...

Keyword(s):

Symmetry Breaking ◽

Brillouin Zone ◽

Translational Symmetry

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Low-dimensional HfS2 as SO2 adsorbent and gas sensor: Effect of water and sulfur vacancies

Physical Chemistry Chemical Physics ◽

10.1039/d1cp04069c ◽

2021 ◽

Author(s):

Amina Bouheddadj ◽

Tarik Ouahrani ◽

Gbèdodé Wilfried KANNHOUNON ◽

Boufatah Reda ◽

Sumeya Bedrane ◽

...

Keyword(s):

Climate Change ◽

Density Functional Theory ◽

Dft Calculations ◽

Gas Sensor ◽

First Principles ◽

Density Functional ◽

Two Dimensional ◽

Functional Theory ◽

Sensor Effect ◽

Low Dimensional

First-principles based on density functional theory (DFT) calculations were performed to investigate the interaction of two-dimensional (2D) HfS2 with SO2, a harmful gas with implications for climate change. In particular,...

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The structure, and electronic and magnetic properties of MX (M=GA, IN; X=S, SE, TE) nanoribbons

International Journal of Modern Physics B ◽

10.1142/s0217979220501684 ◽

2020 ◽

Vol 34 (18) ◽

pp. 2050168

Author(s):

Fei Feng ◽

Fengdong Lv ◽

Gongping Zheng ◽

Guangtao Wang

Keyword(s):

Magnetic Properties ◽

Quantum Confinement ◽

Density Functional ◽

Quantum Confinement Effect ◽

Ring Structure ◽

Functional Theory ◽

Electronic And Magnetic Properties ◽

Semiconductor Behavior ◽

Low Dimensional ◽

Edge Side

We used the first principle of density functional theory to perform detailed calculations regarding the structure, and the electronic and magnetic properties of MX (M[Formula: see text]=[Formula: see text]Ga, In; X[Formula: see text]=[Formula: see text]S, Se, Te) nanoribbons. The armchair nanoribbons (ARNs) are nonmagnetic semiconductors, which have even or odd oscillations of bandgaps. All small-sized zigzag nanoribbons (ZRNs) were found to break the six-membered ring structure and move to the center, thereby exhibiting nonmagnetic semiconductor behavior owing to the quantum confinement effect. However, among the large ZRNs, which are all metals, MTe ZRNs are nonmagnetic; this differs from the case of graphene, MoS2 and Ti2CO2 nanoribbons. MX (M[Formula: see text]=[Formula: see text]Ga, In; X[Formula: see text]=[Formula: see text]S, Se) ZRNs exhibited ferromagnetism owing to the presence of the unpaired electrons on the metal-edge side and the magnetic moment of each pair of molecules, which was controlled by the size of the nanoribbons. The results provided a theoretical reference that can be used in the future to produce MX materials for application in low-dimensional semiconductor devices, spin electron transport devices and new magnetoresistance devices.

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DFT calculations of the structure and stability of copper clusters on MoS2

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.11.30 ◽

2020 ◽

Vol 11 ◽

pp. 391-406

Author(s):

Cara-Lena Nies ◽

Michael Nolan

Keyword(s):

First Principles ◽

Density Functional ◽

Noble Metals ◽

Semiconductor Device ◽

2D Materials ◽

Single Atom ◽

Copper Binding ◽

Adsorption Sites ◽

Potential Applications ◽

Low Dimensional

Layered materials, such as MoS2, are being intensely studied due to their interesting properties and wide variety of potential applications. These materials are also interesting as supports for low-dimensional metals for catalysis, while recent work has shown increased interest in using 2D materials in the electronics industry as a Cu diffusion barrier in semiconductor device interconnects. The interaction between different metal structures and MoS2 monolayers is therefore of significant importance and first-principles simulations can probe aspects of this interaction not easily accessible to experiment. Previous theoretical studies have focused particularly on the adsorption of a range of metallic elements, including first-row transition metals, as well as Ag and Au. However, most studies have examined single-atom adsorption or adsorbed nanoparticles of noble metals. This means there is a knowledge gap in terms of thin film nucleation on 2D materials. To begin addressing this issue, we present in this paper a first-principles density functional theory (DFT) study of the adsorption of small Cu n (n = 1–4) structures on 2D MoS2 as a model system. We find on a perfect MoS2 monolayer that a single Cu atom prefers an adsorption site above the Mo atom. With increasing nanocluster size the nanocluster binds more strongly when Cu atoms adsorb atop the S atoms. Stability is driven by the number of Cu–Cu interactions and the distance between adsorption sites, with no obvious preference towards 2D or 3D structures. The introduction of a single S vacancy in the monolayer enhances the copper binding energy, although some Cu n nanoclusters are actually unstable. The effect of the vacancy is localised around the vacancy site. Finally, on both the pristine and the defective MoS2 monolayer, the density-of-states analysis shows that the adsorption of Cu introduces new electronic states as a result of partial Cu oxidation, but the metallic character of Cu nanoclusters is preserved.

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Atomic origin of spin-valve magnetoresistance at the SrRuO3 grain boundary

National Science Review ◽

10.1093/nsr/nwaa004 ◽

2020 ◽

Vol 7 (4) ◽

pp. 755-762 ◽

Cited By ~ 2

Author(s):

Xujing Li ◽

Li Yin ◽

Zhengxun Lai ◽

Mei Wu ◽

Yu Sheng ◽

...

Keyword(s):

Grain Boundary ◽

Density Functional ◽

Magnetic Moments ◽

Spin Valve ◽

Density Functional Theory Calculations ◽

Precise Knowledge ◽

Transmission Electron ◽

Defect Control ◽

Scanning Transmission ◽

Low Dimensional

Abstract Defects exist ubiquitously in crystal materials, and usually exhibit a very different nature from the bulk matrix. Hence, their presence can have significant impacts on the properties of devices. Although it is well accepted that the properties of defects are determined by their unique atomic environments, the precise knowledge of such relationships is far from clear for most oxides because of the complexity of defects and difficulties in characterization. Here, we fabricate a 36.8° SrRuO3 grain boundary of which the transport measurements show a spin-valve magnetoresistance. We identify its atomic arrangement, including oxygen, using scanning transmission electron microscopy and spectroscopy. Based on the as-obtained atomic structure, the density functional theory calculations suggest that the spin-valve magnetoresistance occurs because of dramatically reduced magnetic moments at the boundary. The ability to manipulate magnetic properties at the nanometer scale via defect control allows new strategies to design magnetic/electronic devices with low-dimensional magnetic order.

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Spontaneous Symmetry Breaking in 5D Conformally Invariant Gravity

Advances in High Energy Physics ◽

10.1155/2016/5353267 ◽

2016 ◽

Vol 2016 ◽

pp. 1-7 ◽

Cited By ~ 2

Author(s):

Taeyoon Moon ◽

Phillial Oh

Keyword(s):

Symmetry Breaking ◽

Spontaneous Symmetry Breaking ◽

Conformal Symmetry ◽

Brane World ◽

Spontaneous Breaking ◽

Warp Factor ◽

Translational Symmetry ◽

Tensor Perturbation ◽

Conformally Invariant ◽

Conformal Quantum Mechanics

We explore the possibility of the spontaneous symmetry breaking in 5D conformally invariant gravity, whose action consists of a scalar field nonminimally coupled to the curvature with its potential. Performing dimensional reduction via ADM decomposition, we find that the model allows an exact solution giving rise to the 4D Minkowski vacuum. Exploiting the conformal invariance with Gaussian warp factor, we show that it also admits a solution which implements the spontaneous breaking of conformal symmetry. We investigate its stability by performing the tensor perturbation and find the resulting system is described by the conformal quantum mechanics. Possible applications to the spontaneous symmetry breaking of time-translational symmetry along the dynamical fifth direction and the brane-world scenario are discussed.

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