Search results for "Computational Mathematic"
showing 10 items of 987 documents
Interstitial carbon defects in silicon. A quantum mechanical characterization through the infrared and Raman spectra.
2021
The infrared (IR) and Raman spectra of eight substitutional carbon defects in silicon are computed at the quantum mechanical level by using a periodic supercell approach based on hybrid functionals, an all electron Gaussian type basis set and the CRYSTAL code. The single substitutional C s case and its combination with a vacancy (C s V and C s SiV) are considered first. The progressive saturation of the four bonds of a Si atom with C is then examined. The last set of defects consists of a chain of adjacent carbon atoms C s i , with i = 1-3. The simple substitutional case, C s , is the common first member of the three sets. All these defects show important, very characteristic features in th…
The modeling of dissimilar welding of immiscible materials by using a phase field method
2013
A multiphysical model of high power beam welding of immiscible materials is developed to explain the influence of operational parameters and materials properties on resulting morphology by simultaneous solving of heat transfer, fluid flow and mass transfer problems. The introduction of phase field description of the interface motion between two immiscible liquids allows obtaining the cartography of melted zone in function of two key-parameters: the position of heat source relatively to joint line and the welding speed. Due to the short thermal cycle limiting mass transfer, high power beam welding techniques may result in very inhomogeneous melted zones. In this study, the interest is paid t…
Origin of pressure-induced insulator-to-metal transition in the van der Waals compound FePS3 from first-principles calculations
2020
The authors acknowledge the assistance of the University Computer Center of Saint‐Petersburg State University in the accomplishment of high‐performance computations. A.K. is grateful to the Latvian Council of Science project no. lzp‐2018/2‐0353 for financial support.
Impact of anionic system modification on the desired properties for CuGa(S1−Se )2 solid solutions
2021
Abstract One of promising directions of the modern solar cells’ development is related to the use of the ternary chalcopyrite crystals (CuInS2, CuGaS2 etc.) and their solid solutions as efficient light absorbing layers. Unfortunately, so far there is no systematic research linking chemical composition to useful properties allowing their optimization to increase the efficiency of solar cells. Therefore, we report the results of the detailed theoretical studies of the structural, electronic, and optical properties for the series of CuGa(S1−xSex)2 solid solutions (x = 0, 0.25, 0.5, 0.75, 1) in the framework of the density functional theory. For this purpose, crystal structures are analyzed wit…
An enhanced grain-boundary framework for computational homogenization and micro-cracking simulations of polycrystalline materials
2015
An enhanced three-dimensional (3D) framework for computational homogenization and intergranular cracking of polycrystalline materials is presented. The framework is aimed at reducing the computational cost of polycrystalline micro simulations, with an aim towards effective multiscale modelling. The scheme is based on a recently developed Voronoi cohesive-frictional grain-boundary formulation. A regularization scheme is used to avoid excessive mesh refinements often induced by the presence of small edges and surfaces in mathematically exact 3D Voronoi morphologies. For homogenization purposes, periodic boundary conditions are enforced on non-prismatic periodic micro representative volume ele…
A three-dimensional grain boundary formulation for microstructural modeling of polycrystalline materials
2013
Abstract A three-dimensional grain boundary formulation is presented for the analysis of polycrystalline microstructures. The formulation is based on a boundary integral representation of the elastic problem for the single grains of the polycrystalline aggregate and it is expressed in terms of the intergranular fields, namely displacements and tractions, that play an important role in polycrystalline micromechanics. The artificial polycrystalline morphology is represented using the Hardcore Voronoi tessellation, which is simple to generate and able to embody the main statistical features of polycrystalline microstructures. The details of the microstructure generation and meshing, which invo…
Structure and dynamics of B2O3 melts and glasses: From ab initio to classical molecular dynamics simulations
2019
Abstract Boron oxide (B2O3) is investigated by a combination of ab initio (DFT-based) molecular dynamics (MD) simulations and classical MD simulations. From the trajectories of the ab initio MD simulation, we derive a three-body interaction potential which is used in classical MD simulations to study various structural and dynamic properties on larger time and length scales than possible in the ab initio simulations. Differences and similarities to the structure and dynamics of other network glass formers such as SiO2 and GeO2 are discussed. Moreover, various properties as obtained from the simulations are compared to those from experiments of B2O3.
Ab initio molecular dynamics simulations of negative thermal expansion in ScF3: the effect of the supercell size
2020
The authors sincerely thank S. Ali, A. Kalinko, and F. Rocca for providing experimental EXAFS data, as well as M. Isupova, V. Kashcheyevs, and A. I. Popov for stimulating discussions. Financial support provided by project No. 1.1.1.2/VIAA/l/16/147 (1.1.1.2/16/I/001) under the activity “Post-doctoral research aid” realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged by D.B. A.K and J.P. would like to thank the support of the Latvian Council of Science project No. lzp-2018/2–0353.
Inverse simulated annealing: Improvements and application to amorphous InSb
2014
An improved inverse simulated annealing method is presented to determine the structure of complex disordered systems from first principles in agreement with available experimental data or desired predetermined target properties. The effectiveness of this method is demonstrated by revisiting the structure of amorphous InSb. The resulting network is mostly tetrahedral and in excellent agreement with available experimental data.
Numerical investigation of the mechanical properties of a novel hybrid polymer composite reinforced with graphene and MXene nanosheets
2020
Abstract This paper presents a numerical investigation of the elastic properties of a novel hybrid polymer composite reinforced with graphene and MXene nanosheets. A finite element computational model was developed to analyze the mechanical properties of a new polymer hybrid composite reinforced with MXene and graphene taking into account the properties of the 2D nanosheets, different aspect ratios, placement options and volume fractions of nanoreinforcements, as well as the interaction effects between the nanofillers and the surrounding polymer matrix. Using the developed numerical model, the influences of the interface layer properties, MXene and graphene aspect ratio, alignment and volum…