scholarly journals Robust quantum-based interatomic potentials for multiscale modeling in transition metals

2006 ◽  
Vol 21 (3) ◽  
pp. 563-573 ◽  
Author(s):  
John A. Moriarty ◽  
Lorin X. Benedict ◽  
James N. Glosli ◽  
Randolph Q. Hood ◽  
Daniel A. Orlikowski ◽  
...  
Keyword(s):  
Transition Metals ◽  
Multiscale Modeling ◽  
Density Functional ◽  
Large Scale ◽  
Dislocation Core ◽  
Dislocation Dynamics ◽  
Interatomic Potentials ◽  
Dynamic Simulations ◽  
Wide Range ◽  
Dynamics Simulations

First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in transition metals and alloys within density-functional quantum mechanics. In the central body-centered cubic (bcc) metals, where multi-ion angular forces are important to materials properties, simplified model GPT (MGPT) potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect, and mechanical properties at both ambient and extreme conditions. Selected applications to multiscale modeling discussed here include dislocation core structure and mobility, atomistically informed dislocation dynamics simulations of plasticity, and thermoelasticity and high-pressure strength modeling. Recent algorithm improvements have provided a more general matrix representation of MGPT beyond canonical bands, allowing improved accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed for dynamic simulations, and the development of temperature-dependent potentials.

scholarly journals A Multi-Scale Modelling of Aggregation of TiO2 Nanoparticle Suspensions in Water

2021 ◽  
Author(s):  
Giulia Mancardi ◽  
Matteo Alberghini ◽  
Neus Aguilera-Porta ◽  
Monica Calatayud ◽  
Pietro Asinari ◽  
...  
Keyword(s):  
Titanium Dioxide ◽  
Density Functional ◽  
Large Scale ◽  
Molecular Descriptors ◽  
Titanium Dioxide Nanoparticles ◽  
Accurate Determination ◽  
Multi Scale ◽  
Spherical Bead ◽  
Living Organisms ◽  
Dynamics Simulations

Titanium dioxide nanoparticles have risen concerns about their possible toxicity and the European Food Safety Authority recently banned the use of TiO2 nano-additive in food products. Following the intent of relating nanomaterials atomic structure with their toxicity without having to conduct large scale experiments on living organisms, we investigate the aggregation of titanium dioxide nanoparticles using a multi-scale technique: starting from ab initio Density Functional Theory to get an accurate determination of the energetics and electronic structure, we switch to classical Molecular Dynamics simulations to calculate the Potential of Mean Force for the connection of two identical nanoparticles in water; the fitting of the latter by a set of mathematical equations is the key for the upscale. Lastly, we perform Brownian Dynamics simulations where each nanoparticle is a spherical bead. This coarsening strategy allows studying the aggregation of a few thousand nanoparticles. Applying this novel procedure, we find three new molecular descriptors, namely, the aggregation free energy and two numerical parameters used to correct the observed deviation from the aggregation kinetic described by the Smoluchowski theory. Molecular descriptors can be fed into QSAR models to predict the toxicity of a material knowing its physicochemical properties, without having to conduct large scale experiments on living organisms.

Atomistic and Continuum Studies of Diffusional Creep and Associated Dislocation Mechanisms in thin Films on Substrates

2003 ◽  
Vol 779 ◽  
Author(s):  
Markus J. Buehler ◽  
Alexander Hartmaier ◽  
Huajian Gao
Keyword(s):  
Thin Films ◽  
Stress Field ◽  
Grain Boundary ◽  
Large Scale ◽  
Strain Relaxation ◽  
Dislocation Dynamics ◽  
Biaxial Stress ◽  
Diffusional Creep ◽  
Material Transport ◽  
Dynamics Simulations

AbstractMotivated by recent theoretical and experimental progress, large-scale atomistic simulations are performed to study plastic deformation in sub-micron thin films. The studies reveal that stresses are relaxed by material transport from the surface into the grain boundary. This leads to the formation of a novel defect identified as diffusion wedge. Eventually, a crack-like stress field develops because the tractions along the grain boundary relax, but the adhesion of the film to the substrate prohibits strain relaxation close to the interface. This causes nucleation of unexpected parallel glide dislocations at the grain boundary-substrate interface, for which no driving force exists in the overall biaxial stress field. The observation of parallel glide dislocations in molecular dynamics studies closes the theory-experiment-simulation linkage. In this study, we also compare the nucleation of dislocations from a diffusion wedge with nucleation from a crack. Further, we present preliminary results of modeling constrained diffusional creep using discrete dislocation dynamics simulations.

scholarly journals First-Principles Prediction of Skyrmionic Phase Behavior in GdFe2 Films Capped by 4d and 5d Transition Metals

2019 ◽  
Vol 9 (4) ◽  
pp. 630 ◽  
Author(s):  
Soyoung Jekal ◽  
Andreas Danilo ◽  
Dao Phuong ◽  
Xiao Zheng
Keyword(s):  
Transition Metals ◽  
Density Functional ◽  
Spin Dynamic ◽  
Zero Magnetic Field ◽  
Spin Orbit Coupling ◽  
Dynamic Simulations ◽  
Functional Theory ◽  
Spin Spiral ◽  
Moriya Interaction ◽  
Spiral Phase

In atomic GdFe 2 films capped by 4d and 5d transition metals, we show that skyrmions with diameters smaller than 12 nm can emerge. The Dzyaloshinskii–Moriya interaction (DMI), exchange energy, and the magnetocrystalline anisotropy (MCA) energy were investigated based on density functional theory. Since DMI and MCA are caused by spin–orbit coupling (SOC), they are increased with 5d capping layers which exhibit strong SOC strength. We discover a skyrmion phase by using atomistic spin dynamic simulations at small magnetic fields of ∼1 T. In addition, a ground state that a spin spiral phase is remained even at zero magnetic field for both films with 4d and 5d capping layers.

Multiscale modeling of plasticity in a copper single crystal deformed at high strain rates

2015 ◽  
Vol 1 (1) ◽  
Author(s):  
Sagar Chandra ◽  
M. K. Samal ◽  
V. M. Chavan ◽  
R. J. Patel
Keyword(s):  
Single Crystal ◽  
Multiscale Modeling ◽  
Crystal Plasticity ◽  
Mechanical Response ◽  
Md Simulations ◽  
Dislocation Dynamics ◽  
Copper Single Crystal ◽  
Deformation Response ◽  
Discrete Dislocation ◽  
Dynamics Simulations

AbstractA hierarchical multiscale modeling approach is presented to predict the mechanical response of dynamically deformed (1100 s−1−4500 s−1) copper single crystal in two different crystallographic orientations.Anattempt has been made to bridge the gap between nano-, micro- and meso- scales. In view of this, Molecular Dynamics (MD) simulations at nanoscale are performed to quantify the drag coefficient for dislocations which has been exploited in Dislocation Dynamics (DD) regime at the microscale. Discrete dislocation dynamics simulations are then performed to calculate the hardening parameters required by the physics based Crystal Plasticity (CP) model at the mesoscale. The crystal plasticity model employed is based on thermally activated theory for plastic flow. Crystal plasticity simulations are performed to quantify the mechanical response of the copper single crystal in terms of stressstrain curves and shape changes under dynamic loading. The deformation response obtained from CP simulations is in good agreement with the experimental data.

scholarly journals Periodic Boundary Conditions for Dislocation Dynamics Simulations in Three Dimensions

2000 ◽  
Vol 653 ◽  
Author(s):  
Vasily V. Bulatov ◽  
Moon Rhee ◽  
Wei Cai
Keyword(s):  
Boundary Conditions ◽  
Large Scale ◽  
Periodic Boundary ◽  
Periodic Boundary Conditions ◽  
Dislocation Dynamics ◽  
Three Dimensions ◽  
Translational Invariance ◽  
Timing Data ◽  
Dynamics Simulations ◽  
Consistent Treatment

AbstractThis article presents an implementation of periodic boundary conditions (PBC) for Dislocation Dynamics (DD) simulations in three dimensions (3D). We discuss fundamental aspects of PBC development, including preservation of translational invariance and line connectivity, the choice of initial configurations compatible with PBC and a consistent treatment of image stress. On the practical side, our approach reduces to manageable proportions the computational burden of updating the long-range elastic interactions among dislocation segments. The timing data confirms feasibility and practicality of PBC for large-scale DD simulations in 3D.

scholarly journals Molecular Dynamics Studies of the Melting of Copper with Vacancies amd Dislocations at High Pressures

MRS Advances ◽  
2017 ◽  
Vol 2 (48) ◽  
pp. 2597-2602 ◽  
Author(s):  
Clarence C Matthai ◽  
Jessica Rainbow
Keyword(s):  
Molecular Dynamics ◽  
Melting Temperature ◽  
Large Scale ◽  
High Pressures ◽  
Defect Density ◽  
Melting Process ◽  
Interatomic Potentials ◽  
Embedded Atom ◽  
Line Defects ◽  
Dynamics Simulations

ABSTRACTMolecular dynamics simulations of the melting process of bulk copper were performed using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) with the interatomic potentials being described by the embedded atom method. The aim of the study was to understand the effects of high pressures and defects on the melting temperature. The simulations were visualised using Visual Molecular Dynamics (VMD). The melting temperature of a perfect copper crystal, was found to be slightly higher than the experimentally observed value. The melting temperature as a function of pressure was determined and compared with experiment. Point and line defects, in the form of dislocations, were then introduced into crystal and the new melting temperature of the crystal determined. We find that the melting temperature decreases as the defect density is increased. Additionally, the slope of the melting temperature curve was found to decrease as the pressure was increased while the vacancy formation energy increases with pressure.

New Technique for AB Initio Atomistic Potentials and Application to Thermal Expansion of Ni/Cr Alloys

1992 ◽  
Vol 291 ◽  
Author(s):  
J. Mei ◽  
B.R. Cooper ◽  
Y.G. Hao ◽  
S.P. Lim ◽  
F.L. VanScoy
Keyword(s):  
Thermal Expansion ◽  
Ab Initio ◽  
Density Functional ◽  
Interatomic Potential ◽  
Coefficient Of Thermal Expansion ◽  
Many Body ◽  
Functional Theory ◽  
Transition Metal Alloys ◽  
Wide Range ◽  
Dynamics Simulations

ABSTRACTA scheme of developing ab initio many body potentials based on total energy calculations within density functional theory (DFT) is presented and demonstrated for transition metal alloys. An ab initio interatomic potential for Ni/Cr alloys is constructed with no input from experimental data. Molecular dynamics simulations have been performed to study thermal expansions. The coefficient of thermal expansion (CTE) has been calculated over a wide range of temperature, and good agreement is obtained between theory and experiment.

Hydrogen Storage in Carbon Nanotubes: A Multi-Scale Theoretical Study

2006 ◽  
Vol 6 (1) ◽  
pp. 87-90 ◽  
Author(s):  
Giannis Mpourmpakis ◽  
Emmanuel Tylianakis ◽  
George Froudakis
Keyword(s):  
Carbon Nanotubes ◽  
Hydrogen Storage ◽  
Density Functional ◽  
Large Scale ◽  
Hydrogen Diffusion ◽  
Theoretical Study ◽  
Multi Scale ◽  
Hydrogen Interaction ◽  
Dynamics Simulations ◽  
Walled Carbon Nanotubes

A Combination of quantum and classical calculations has been performed to investigate the hydrogen storage in single-walled carbon nanotubes (SWNTs). The ab-initio calculations at the Density Functional level of Theory (DFT) show the nature of hydrogen interaction in selected sites of a (5,5) tube walls. On top of this, Molecular Dynamics simulations model large scale nanotube systems and reproduce the storage capacity under variant temperature conditions. Our results indicate that the interaction of hydrogen with SWNTs is very weak and slightly increase of temperature, causes hydrogen diffusion from the tube walls.

Computer simuations for the nano-scale

2007 ◽  
Vol 57 (1) ◽  
pp. 1-176 ◽  
Author(s):  
I. Štich
Keyword(s):  
Quantum Monte Carlo ◽  
Density Functional ◽  
Large Scale ◽  
Hartree Fock ◽  
Monte Carlo Techniques ◽  
Nano Scale ◽  
Scale Modeling ◽  
Starting Point ◽  
Wide Range ◽  
Weak Points

Computer simuations for the nano-scaleA review of methods for computations for the nano-scale is presented. The paper should provide a convenient starting point into computations for the nano-scale as well as a more in depth presentation for those already working in the field of atomic/molecular-scale modeling. The argument is divided in chapters covering the methods for description of the (i) electrons, (ii) ions, and (iii) techniques for efficient solving of the underlying equations. A fairly broad view is taken covering the Hartree-Fock approximation, density functional techniques and quantum Monte-Carlo techniques for electrons. The customary quantum chemistry methods, such as post Hartree-Fock techniques, are only briefly mentioned. Description of both classical and quantum ions is presented. The techniques cover Ehrenfest, Born-Oppenheimer, and Car-Parrinello dynamics. The strong and weak points of both principal and technical nature are analyzed. In the second part we introduce a number of applications to demonstrate the different approximations and techniques introduced in the first part. They cover a wide range of applications such as non-simple liquids, surfaces, molecule-surface interactions, applications in nanotechnology, etc. These more in depth presentations, while certainly not exhaustive, should provide information on technical aspects of the simulations, typical parameters used, and ways of analysis of the huge amounts of data generated in these large-scale supercomputer simulations.

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