| 1. |
- Abrikossov, Alexei
(author)
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Modelling anisotropic interactions in colloidal systems
- 2017
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Doctoral thesis (other academic/artistic)abstract
- There has been an increased interest to design “smart materials” which can self-assemble into complex structures in accordance to external factors such as for example electromagnetic fields. By designing particles with directional interactions one is able to control how particles will interact with each other. By means of both Monte Carlo and Molecular Dynamics simulations we study the interactions of three distinct types of models namely the self-assembly of off-centered dipoles, the charged patchy particle model in multivalent electrolytes, and an all atom model of [3,3Õ-cobalt(III) bis(1.2-dicarbollide)] and its interaction with solvent. Besides this there is also a short discussion about the long-range anisotropic interactions and ways by which one can calculate them.
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| 2. |
- Abrikossov, Alexei, et al.
(author)
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Self-assembly of spherical colloidal particles with off-centered magnetic dipoles
- 2013
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 9:37, s. 8904-8913
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Journal article (peer-reviewed)abstract
- Fluids of spherical colloids possessing an off-centered embedded magnetic dipole were investigated by using Monte Carlo simulations. Systems of colloids with different strengths and directions of the embedded dipole moment confined in a 2D space without and with an external magnetic field applied were considered. The fluids were characterized by radial distribution functions, angular distribution functions, cluster data, and energetic data. In the absence of an external field, the colloids form dimers and trimers at sufficiently large magnetic moment without the tendency of forming chains of colloids as appearing in systems with particles possessing a central magnetic dipole. In the presence of an external field, chains of colloids aligned in a zigzag fashion were formed for a field parallel to the plane of the particles, whereas the colloidal ordering was suppressed in the presence of a field perpendicular to that plane. The findings agree surprisingly well with the recent experimental observations on fluids containing spherical polymer colloids with embedded single-domain magnetic hematite cubes (S. Sacanna, L. Rossi, and D. J. Pine, J. Am. Chem. Soc., 2012, 134, 6112).
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| 3. |
- Abrikossov, Alexei, et al.
(author)
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Steering patchy particles using multivalent electrolytes
- 2017
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 13:26, s. 4591-4597
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Journal article (peer-reviewed)abstract
- Proteins and many recently designed colloids can be regarded as patchy particles where directional interactions strongly influence and govern assembly behavior. Using explicit ion implicit solvent Metropolis Monte Carlo simulations, we investigate spherical model particles, carrying both charge and electric patches, in dilute aqueous 1 : 1, 1 : 3, and 3 : 1 electrolyte solutions. Striking differences in pair interaction free energies and orientational correlations are induced by three different salts which are discussed and rationalized in terms of ion-binding to surface groups, ion-ion correlations, and double layer forces. These findings suggest a general strategy where directional, intermolecular interactions can be invoked and tuned via small amounts of a carefully chosen electrolyte.
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| 4. |
- Bykov, Maxim, et al.
(author)
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High-Pressure Synthesis of Dirac Materials: Layered van der Waals Bonded BeN4 Polymorph
- 2021
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In: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 126:17
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Journal article (peer-reviewed)abstract
- High-pressure chemistry is known to inspire the creation of unexpected new classes of compounds with exceptional properties. Here, we employ the laser-heated diamond anvil cell technique for synthesis of a Dirac material BeN4. A triclinic phase of beryllium tetranitride tr-BeN4 was synthesized from elements at similar to 85 GPa. Upon decompression to ambient conditions, it transforms into a compound with atomic-thick BeN4 layers interconnected via weak van der Waals bonds and consisting of polyacetylene-like nitrogen chains with conjugated pi systems and Be atoms in square-planar coordination. Theoretical calculations for a single BeN4 layer show that its electronic lattice is described by a slightly distorted honeycomb structure reminiscent of the graphene lattice and the presence of Dirac points in the electronic band structure at the Fermi level. The BeN4 layer, i.e., beryllonitrene, represents a qualitatively new class of 2D materials that can be built of a metal atom and polymeric nitrogen chains and host anisotropic Dirac fermions.
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| 5. |
- Casillas Trujillo, Luis, et al.
(author)
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Experimental and theoretical evidence of charge transfer in multi-component alloys : how chemical interactions reduce atomic size mismatch
- 2021
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In: Materials Chemistry Frontiers. - : Royal Society of Chemistry. - 2052-1537. ; 5:15, s. 5746-5759
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Journal article (peer-reviewed)abstract
- Ab initio simulations of a multi-component alloy using density functional theory (DFT) were combined with experiments on thin films of the same material using X-ray photoelectron spectroscopy (XPS) to study the connection between the electronic and atomic structures of multi-component alloys. The DFT simulations were performed on an equimolar HfNbTiVZr multi-component alloy. Structure and charge transfer were evaluated using relaxed, non-relaxed, as well as elemental reference structures. The use of a fixed sphere size model allowed quantification of charge transfer, and separation into different contributions. The charge transfer was generally found to follow electronegativity trends and results in a reduced size mismatch between the elements, and thus causes a considerable reduction of the lattice distortions compared to a traditional assumption based on tabulated atomic radii. A calculation of the average deviation from the average radius (i.e. the so-called δ-parameter) based on the atomic Voronoi volumes gave a reduction of δ from ca. 6% (using the volumes in elemental reference phases) to ca. 2% (using the volumes in the relaxed multi-component alloy phase). The reliability of the theoretical results was confirmed by XPS measurements of a Hf22Nb19Ti18V19Zr21 thin film deposited by sputter deposition. The experimentally observed core level binding energy shifts (CLS), as well as peak broadening due to a range of chemical surroundings, for each element showed good agreement with the calculated DFT values. The single solid solution phase of the sample was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) including energy dispersive spectroscopy (EDS) with nm-resolution. These observations show that the HfNbTiVZr solid solution phase is non-ideal, and that chemical bonding plays an important part in the structure formation, and presumably also in the properties. Our conclusions should be transferable to other multi-component alloy systems, as well as some other multi-component material systems, and open up interesting possibilities for the design of material properties via the electronic structure and controlled charge transfer between selected metallic elements in the materials.
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| 6. |
- Stenqvist, Björn, et al.
(author)
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Direct summation of dipole-dipole interactions using the Wolf formalism
- 2015
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 143:1
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Journal article (peer-reviewed)abstract
- We present an expanded Wolf formalism for direct summation of long-range dipole-dipole interactions and rule-of-thumbs how to choose optimal spherical cutoff (R-c) and damping parameter (alpha). This is done by comparing liquid radial distribution functions, dipole-dipole orientation correlations, particle energies, and dielectric constants, with Ewald sums and the Reaction field method. The resulting rule states that alpha sigma < 1 and alpha R-c > 3 for reduced densities around rho* = 1 where sigma is the particle size. Being a pair potential, the presented approach scales linearly with system size and is applicable to simulations involving point dipoles such as the Stockmayer fluid and polarizable water models. (C) 2015 AIP Publishing LLC.
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