This document summarizes research on using ab initio modeling and multiscale simulations to design new materials. It discusses how density functional theory can be used to calculate material properties from first principles and inform higher scale simulations. Examples are given of designing titanium alloys for biomedical implants, high strength steels, soft magnetic steels, magnesium alloys, and chitin composites by predicting properties like elastic modulus from the electronic structure of the materials.
Plenary lecture of the XIV SBPMat Meeting, given by Prof. Nader Engheta (University of Pennsylvania) on September 28, 2015, in Rio de Janeiro (Brazil).
Plenary lecture given by Prof. Hajo Freund (Fritz-Haber-Institut der Max-Planck-Gesellschaft, Germany) on September 11, 2017 in Gramado (Brazil) during the XVI B-MRS Meeting.
Plenary lecture of the XIV SBPMat Meeting, given by Prof. Nader Engheta (University of Pennsylvania) on September 28, 2015, in Rio de Janeiro (Brazil).
Plenary lecture given by Prof. Hajo Freund (Fritz-Haber-Institut der Max-Planck-Gesellschaft, Germany) on September 11, 2017 in Gramado (Brazil) during the XVI B-MRS Meeting.
Proslier - Localized magnetism on the Surface of Niobium: experiments and theorythinfilmsworkshop
http://www.surfacetreatments.it/thinfilms
Localized magnetism on the surface of Niobium: experiments and theory (Thomas Proslier - 40')
Speaker: Thomas Proslier - Argonne National Laboratory | Duration: 40 min.
Abstract
The presence of magnetic impurities in native niobium oxides have been confirmed by Point contact spectroscopy (PCT), SQUID magnetometry and Electron paramagnetic resonance (EPR). All niobium (Nb) samples displayed a small impurity contribution to the magnetic susceptibility at low temperatures which exhibited Curie-Weiss behavior, indicative of weakly coupled localized paramagnetic moments. By examining Nb samples with widely varying surface-to-volume ratios (rods, foils, wires, powders) it was found that the impurity contribution is correlated with surface area. Tunneling measurements which utilize the native oxide layers as barriers exhibit a zero-bias conductance peak which splits in a magnetic field > 4T, consistent with the Appelbaum-Anderson model for spin flip tunneling. Viewed together, the experiments strongly suggest that the native oxides of Nb are intrinsically defective, and consistently exhibit localized paramagnetic moments, likely caused by oxygen vacancies in Nb2O5. The computation of the surface impedance (RS) in presence of magnetic impurities in the Shiba approximation reveals the saturation at low temperature of Rs, suggesting that magnetic impurities are responsible for the so-called residual resistance.
Plenary lecture - XV B-MRS Meeting - Campinas, SP, Brazil - September, 25 to 29, 2016.
Author: Elvira Fortunato (CENIMAT, Universidade Nova de Lisboa, Portugal).
The broad lined_type_ic_sn_2012_ap_and_the_nature_of_relatvistic_supernovae_l...Sérgio Sacani
Artigo mostra como os astrônomos deduziram que a supernova SN 2012ap, é o elo perdido que faltava para a construção completa da árvore genealógica das supernovas.
Metal ion burst: Examining metal ion diffusion using ultrafast fluorescence s...Chelsey Crosse
Presentation to accompany my report for my oral examination. Details background of fluorescence upconversion techniques, development of measurement systems for release of a metal cation and minimization of diffusion distribution in solutions.
Influence of concentration on the structural, optical and electrical properti...iosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Database of Topological Materials and Spin-orbit SpillageKAMAL CHOUDHARY
We present the results of a high-throughput, first principles search for topological materials based on identifying materials with band inversion induced by spin-orbit coupling. Out of the currently available 30000 materials in our database, we investigate more than 4507 non-magnetic materials having heavy atoms and low bandgaps. We compute the spillage between the spin-orbit and non-spin-orbit wave functions, resulting in more than 1699 high-spillage candidate materials. We demonstrate that in addition to Z2 topological insulators, this screening method successfully identifies many semimetals and topological crystalline insulators. Our approach is applicable to the investigation of disordered or distorted materials, because it is not based on symmetry considerations, and it can be extended to magnetic materials. After our first screening step, we use Wannier-interpolation to calculate the topological invariants and to search for band crossings in our candidate materials. We discuss some individual example materials, as well as trends throughout our dataset, that is available at JARVIS-DFT website: http://jarvis.nist.gov
Plenary lecture of the XIII SBPMat (Brazilian MRS) meeting, given on October 1st 2014 in João Pessoa (Brazil) by Roberto Dovesi, professor at Universita' degli Studi di Torino (Italy).
> Discovery of LaCl3:Ce, LaBr3:Ce led to a new era in halide scintillator research
- CeBr3, SrI2:Eu, Tl2LaCl5:Ce, others
- Elpasolites (CLYC, CLLBC, Tl-elpasolites)
Li-containing elpasolites provide combined gamma-neutron detection, with chlorides adding fast neutron spectroscopic capabilities
> Several new scintillators provide gamma-resolution of ≤3% (FWHM)
> Modulation of proportionality a new trend in scintillator optimization
> Organic crystals, plastics and organic-inorganic composites with gamma-neutron PSD attractive for multimode, low cost, large systems
> Ceramic scintillators promising for high energy radiography and PET
> Commercialization of some of the promising candidates underway.
N. Herbots' CIMD Clean Room Lab
http://ceaspub.eas.asu.edu/phy132/herbots.htm
US Patents 6,613,677 (9/2/03), 5,241,214, 4,800,100
IBeam User facility where CIMD lab is located
http://www.ibeam.asu.edu/
Class web page:
PHY 121 http://phyastweb.la.asu.edu/classes/phy121-herbots/
PHY 131 http://phyastweb.la.asu.edu/phy131-herbots/
PHY 334 http://phyastweb.la.asu.edu/phy334-herbots/
Python for Science and Engineering: a presentation to A*STAR and the Singapor...pythoncharmers
An introduction to Python in science and engineering.
The presentation was given by Dr Edward Schofield of Python Charmers (www.pythoncharmers.com) to A*STAR and the Singapore Computational Sciences Club in June 2011.
Proslier - Localized magnetism on the Surface of Niobium: experiments and theorythinfilmsworkshop
http://www.surfacetreatments.it/thinfilms
Localized magnetism on the surface of Niobium: experiments and theory (Thomas Proslier - 40')
Speaker: Thomas Proslier - Argonne National Laboratory | Duration: 40 min.
Abstract
The presence of magnetic impurities in native niobium oxides have been confirmed by Point contact spectroscopy (PCT), SQUID magnetometry and Electron paramagnetic resonance (EPR). All niobium (Nb) samples displayed a small impurity contribution to the magnetic susceptibility at low temperatures which exhibited Curie-Weiss behavior, indicative of weakly coupled localized paramagnetic moments. By examining Nb samples with widely varying surface-to-volume ratios (rods, foils, wires, powders) it was found that the impurity contribution is correlated with surface area. Tunneling measurements which utilize the native oxide layers as barriers exhibit a zero-bias conductance peak which splits in a magnetic field > 4T, consistent with the Appelbaum-Anderson model for spin flip tunneling. Viewed together, the experiments strongly suggest that the native oxides of Nb are intrinsically defective, and consistently exhibit localized paramagnetic moments, likely caused by oxygen vacancies in Nb2O5. The computation of the surface impedance (RS) in presence of magnetic impurities in the Shiba approximation reveals the saturation at low temperature of Rs, suggesting that magnetic impurities are responsible for the so-called residual resistance.
Plenary lecture - XV B-MRS Meeting - Campinas, SP, Brazil - September, 25 to 29, 2016.
Author: Elvira Fortunato (CENIMAT, Universidade Nova de Lisboa, Portugal).
The broad lined_type_ic_sn_2012_ap_and_the_nature_of_relatvistic_supernovae_l...Sérgio Sacani
Artigo mostra como os astrônomos deduziram que a supernova SN 2012ap, é o elo perdido que faltava para a construção completa da árvore genealógica das supernovas.
Metal ion burst: Examining metal ion diffusion using ultrafast fluorescence s...Chelsey Crosse
Presentation to accompany my report for my oral examination. Details background of fluorescence upconversion techniques, development of measurement systems for release of a metal cation and minimization of diffusion distribution in solutions.
Influence of concentration on the structural, optical and electrical properti...iosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Database of Topological Materials and Spin-orbit SpillageKAMAL CHOUDHARY
We present the results of a high-throughput, first principles search for topological materials based on identifying materials with band inversion induced by spin-orbit coupling. Out of the currently available 30000 materials in our database, we investigate more than 4507 non-magnetic materials having heavy atoms and low bandgaps. We compute the spillage between the spin-orbit and non-spin-orbit wave functions, resulting in more than 1699 high-spillage candidate materials. We demonstrate that in addition to Z2 topological insulators, this screening method successfully identifies many semimetals and topological crystalline insulators. Our approach is applicable to the investigation of disordered or distorted materials, because it is not based on symmetry considerations, and it can be extended to magnetic materials. After our first screening step, we use Wannier-interpolation to calculate the topological invariants and to search for band crossings in our candidate materials. We discuss some individual example materials, as well as trends throughout our dataset, that is available at JARVIS-DFT website: http://jarvis.nist.gov
Plenary lecture of the XIII SBPMat (Brazilian MRS) meeting, given on October 1st 2014 in João Pessoa (Brazil) by Roberto Dovesi, professor at Universita' degli Studi di Torino (Italy).
> Discovery of LaCl3:Ce, LaBr3:Ce led to a new era in halide scintillator research
- CeBr3, SrI2:Eu, Tl2LaCl5:Ce, others
- Elpasolites (CLYC, CLLBC, Tl-elpasolites)
Li-containing elpasolites provide combined gamma-neutron detection, with chlorides adding fast neutron spectroscopic capabilities
> Several new scintillators provide gamma-resolution of ≤3% (FWHM)
> Modulation of proportionality a new trend in scintillator optimization
> Organic crystals, plastics and organic-inorganic composites with gamma-neutron PSD attractive for multimode, low cost, large systems
> Ceramic scintillators promising for high energy radiography and PET
> Commercialization of some of the promising candidates underway.
N. Herbots' CIMD Clean Room Lab
http://ceaspub.eas.asu.edu/phy132/herbots.htm
US Patents 6,613,677 (9/2/03), 5,241,214, 4,800,100
IBeam User facility where CIMD lab is located
http://www.ibeam.asu.edu/
Class web page:
PHY 121 http://phyastweb.la.asu.edu/classes/phy121-herbots/
PHY 131 http://phyastweb.la.asu.edu/phy131-herbots/
PHY 334 http://phyastweb.la.asu.edu/phy334-herbots/
Python for Science and Engineering: a presentation to A*STAR and the Singapor...pythoncharmers
An introduction to Python in science and engineering.
The presentation was given by Dr Edward Schofield of Python Charmers (www.pythoncharmers.com) to A*STAR and the Singapore Computational Sciences Club in June 2011.
NAMRC 2016_build height effect on the inconel 718 parts fabricated by selecti...Xiaoqing Wang
Full Paper:
X. Wang, T. Keya, K. Chou, Build Height Effect on the Inconel 718 Parts Fabricated by Selective Laser Melting, Procedia Manuf. 5 (2016) 1006–1017. doi:10.1016/j.promfg.2016.08.089.
Available at:
https://www.academia.edu/29967061/Build_Height_Effect_on_the_Inconel_718_Parts_Fabricated_by_Selective_Laser_Melting
SWCNT Growth from Chiral and Achiral Carbon Nanorings: Prediction of Chiralit...Stephan Irle
Catalyst-free, chirality-controlled growth of chiral and achiral single-walled carbon nanotubes (SWCNTs) from organic precursors is demonstrated using quantum chemical simulations [1]. Growth of (4,3), (6,5), (6,1), (10,1), (6,6) and (8,0) SWCNTs was induced by ethynyl radical (C2H) addition to organic precursors. These simulations show a strong dependence of the SWCNT growth rate on the chiral angle, θ. The SWCNT diameter however does not influence the SWCNT growth rate under these conditions. This agreement with a previously proposed screw-dislocation-like model of transition metal-catalyzed SWCNT growth rates [2] indicates that the SWCNT growth rate is an intrinsic property of the SWCNT edge itself. Conversely, we predict that the rate of local SWCNT growth via Diels-Alder cycloaddition of C2H2 is strongly influenced by the diameter of the SWCNT. We therefore predict the existence of a maximum local growth rate for an optimum diameter/chirality combination at a given C2H/C2H2 ratio. We also find that the ability of a SWCNT to avoid defect formation during growth is an intrinsic quality of the SWCNT edge.
References:
[1] Li, H.-B.; Page, A. J.; Irle, S.; Morokuma, K. J. Am. Chem. Soc. 2012, 134, 15887-15896.
[2] Ding, F.; Harutyunyan, A. R.; Yakobson, B. I. Proc. Natl. Acad. Sci. 2009, 106, 2506-2509.
What can we learn from molecular dynamics simulations of carbon nanotube and ...Stephan Irle
We present the results of nonequilibrium molecular dynamics (MD) simulations of catalytic and non-catalytic carbon nanostructure formation processes, including single-walled carbon nanotube (SWCNT) and graphene nucleation and growth. In the talk, we discuss the significance of the findings in the light of more traditional, static descriptions of growth reaction mechanisms, and highlight differences as well as commonalities.
2018-11-26 Investigation of the band structure of quantum wells based on gapl...LeonidBovkun
The present PhD thesis primarily aims at filling some of existing gaps in our understanding of the electronic band structure in 2D and quasi-2D heterostructures based on HgTe/HgCdTe and InAs/InSb materials, which both may be tuned into topologically insulating phase using particular structural parameter. To explore their properties, the primal experimental technique, infrared and THz magneto-spectroscopy operating in a broad of magnetic fields, is combined with complementary magneto-transport measurements. This combination of experimental methods allows us to get valuable insights into electronic states not only at the Fermi energy, but also in relatively broad vicinity.
Prof Ong gave a webinar talk on the AI Revolution in Materials Science for the Singapore Agency of Science Technology and Research (A*STAR). In this talk, he discussed the big challenges in materials science where AI can potentially make a huge impact towards addressing as well as outstanding challenges and opportunities to bringing forth the AI revolution to the materials domain.
Microstructural and Dielectric Characterization of Sr doped Ba(Fe0.5Ta0.5)O3 ...theijes
Solid state reaction method was used to synthesize Ba1-xSrx(Fe0.5Ta0.5)O3 ceramic(x=0, 0.1, 0.2, 0.3, 0.4 and 0.5). The raw materials of making Sr doped Ba(Fe0.5Ta0.5)O3 were BaCO3, SrCO3, Fe2O3, Ta2O5 (purity better than 99%). Pellet and ring shaped samples prepared from each composition were sintered at 1400 and 1450ºC for 5 hour. The phase formation of Ba1-xSrx(Fe0.5Ta0.5)O3 was checked using X-ray diffraction (XRD) technique and observed a cubic perovskite crystal structure in space group Pm3m (221). Microstructure of the individual compound was examined by the field emission scanning electron micrograph (FESEM). Grain size was found to be varied with Sr content. The lattice parameter decreased with increasing Sr content. Dielectric spectroscopy was applied to investigate the electrical properties of BSFT at room temperature and in a frequency range of 100Hz–100 MHz. An analysis of the dielectric constant εʹ and loss tangent tan with frequency was performed assuming a distribution of relaxation times. The low frequency dielectric dispersion corresponds to the DC electrical conductivity.
Analysis Of Carbon Nanotubes And Quantum Dots In A Photovoltaic Device Slide ...M. Faisal Halim
Francis' presentation to Louis Stokes Association for Minority Participation. Since I co-authored this work I think I have the right to a copy. I was the graduate student Francis was working with.
Overview combining ab initio with continuum theoryDierk Raabe
Multi-methodological approaches combining quantum-mechanical and/or atomistic simulations
with continuum methods have become increasingly important when addressing multi-scale phenomena in
computational materials science. A crucial aspect when applying these strategies is to carefully check,
and if possible to control, a variety of intrinsic errors and their propagation through a particular multimethodological
scheme. The first part of our paper critically reviews a few selected sources of errors
frequently occurring in quantum-mechanical approaches to materials science and their multi-scale propagation
when describing properties of multi-component and multi-phase polycrystalline metallic alloys.
Our analysis is illustrated in particular on the determination of i) thermodynamic materials properties at
finite temperatures and ii) integral elastic responses. The second part addresses methodological challenges
emerging at interfaces between electronic structure and/or atomistic modeling on the one side and selected
continuum methods, such as crystal elasticity and crystal plasticity finite element method (CEFEM and
CPFEM), new fast Fourier transforms (FFT) approach, and phase-field modeling, on the other side.
Dislocation and twin substructure evolution during strain hardening of an Fe–22 wt.% Mn–0.6 wt.% C TWIP steel observed by electron channeling contrast imaging
Investigation of the indentation size effect through the measurement of the geometrically necessary dislocations beneath small indents
of different depths using EBSD tomography
Imaging of dislocations and twins in TWIP steels using electron channeling contrast imaging under controlled diffraction conditions in a scanning electron microscope
High manganese conference korea twip steelDierk Raabe
Lecture about the effects of strain path and crystallographic texture on microstructure in Fe–22 wt.% Mn–0.6 wt.% C TWIP steels using Electron Channeling Contrast Imaging (ECCI) and EBSD
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
Objective:
Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
Francesca Gottschalk - How can education support child empowerment.pptxEduSkills OECD
Francesca Gottschalk from the OECD’s Centre for Educational Research and Innovation presents at the Ask an Expert Webinar: How can education support child empowerment?
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Introduction to AI for Nonprofits with Tapp NetworkTechSoup
Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
Ab initio simulation in materials science, Dierk Raabe, lecture at IHPC Singapore
1. D. Raabe, F. Roters, P. Eisenlohr, H. Fabritius, S. Nikolov, M. Petrov
O. Dmitrieva, T. Hickel, M. Friak, D. Ma, J. Neugebauer
Düsseldorf, Germany
WWW.MPIE.DE
d.raabe@mpie.de
IHPC - Institute for High Performance Computing Singapore 1. Nov 2010 Dierk Raabe
Using ab-initio based multiscale models and
experiments for alloy design
12. Time-independent Schrödinger equation
h/(2p)
Many particles (stationary formulation)
Square |y(r)|2 of wave function y(r) of a particle at given position r = (x,y,z)
is a measure of probability to observe it there
Raabe: Adv. Mater. 14 (2002)
13. i electrons: mass me ; charge qe = -e ; coordinates rei
j atomic cores:mass mn ; charge qn = ze ; coordinates rnj
Time-independent Schrödinger equation for many particles
Raabe: Adv. Mater. 14 (2002)
15. Hohenberg-Kohn-Sham theorem:
Ground state energy of a many body system definite function of its particle density
Functional E(n(r)) has minimum with respect to variation in particle position at
equilibrium density n0(r)
Chemistry Nobelprice 1998
Hohenberg Kohn, Phys. Rev. 136 (1964) B864
16. Total energy functional
T(n) kinetic energy
EH(n) Hartree energy (electron-electron repulsion)
Exc(n) Exchange and correlation energy
U(r) external potential
Exact form of T(n) and Exc(n) unknown
Hohenberg Kohn, Phys. Rev. 136 (1964) B864
17. Local density approximation – Kohn-Sham theory
Parametrization of particle density by a set of ‘One-electron-orbitals‘
These form a non-interacting reference system (basis functions)
2
i
i rrn
Calculate T(n) without consideration of interactions
rdr
m2
rnT 2
i
i
2
2
*
i
Determine optimal basis set by variational principle
0
r
rnE
i
Hohenberg Kohn, Phys. Rev. 136 (1964) B864
34. 33
Mn atoms
Ni atoms
Mn iso-concentration surfaces at 18 at.%
APT results: Atomic map (12MnPH aged 450°C/48h)
70 million ions
Laser mode
(0.4nJ, 54K)
Dmitrieva et al., Acta Mater, in press 2010
Martensite decorated by precipitations
Austenite
?
?
35. M A
Mn layer 1
Mn layer 2
34
Mn layer2
Mn layer 1
Mn iso-concentration surfaces at 18 at.%
Thermo-Calc
Phase equilibrium Mn-contents:
27 at. % Mn in austenite (A)
3 at. % Mn in ferrite (martensite) (M)
1D profile: step size 0.5 nm
M A M
depletion zone
nominal 12 at.% Mn
APT results: chemical profiles
Dmitrieva et al., Acta Mater, in press 2010
36. 35
precipitates in a`
no precipitates in
12MnPH after aging (48h 450°C)
nmDtxDiff 302
nmxDiff 2
Raabe, Ponge, Dmitrieva, Sander: Adv. Eng. Mat. 11 (2009) 547
37. Mean diffusion path of Mn in austenite
(aging 450°C/48h) 2 nm
36
M A
Mn layer 1
Mn layer 2
nominal 12 at.%
Thermo-Calc
Phase equilibrium Mn content:
27 at. % in austenite
3 at. % in ferrite (martensite)
10 nm
Ti, Si,
Mo
Mn-rich
layer
AM
PB migration
Mn diffusion
phase boundary
aging
New
austenite
(formed
during
aging)
DICTRA
AM
original position
phase boundary
final position
phase boundary
APT results and simulation: DICTRA/ThermoCalc
Dmitrieva et al., Acta Mater, in press 2010
39. 38
Nano-precipitates in soft magnetic steels
size Cu precipitates (nm)
{JP 2004 339603}
15 nm
magneticloss(W/kg)
Fe-Si steel with Cu nano-precipitates
nanoparticles too small for Bloch-wall interaction but
effective as dislocation obstacles
mechanically very strong soft magnets for motors
40. 39
Cu 2 wt.%
20 nm
120 min
20 nm
6000 min
Iso-concentration
surfaces for
Cu 11 at.%
Fe-Si-Cu, LEAP 3000X HR analysis
Fe-Si steel with Cu nano-precipitates
450°C aging
47. 46
For neighbor interaction energy take
difference (in eV)
(repulsive) = 0.390
(attractive) = -0.124
(attractive) = -0.245
E SiSi
bin
E S iCu
bin
E CuCu
bin
Ab-initio, binding energies
Fe-Si steel with Cu nano-precipitates
65. 64Sachs, Fabritius, Raabe: Journal of Structural Biology 161 (2008) 120
Structure hierarchy of chitin-compounds
Nikolov et al.: Adv. Mater. 22 (2010) p. 519; Al-Sawalmih et al.: Adv. Funct. Mater. 18 (2008) p. 3307 Fabritius et al.: Adv. Mater. 21 (2009) 391
66. 65
P218.96 35.64 19.50 90˚α-Chitin
Space group
Unit cell dimensions (Bohrradius)
a b c γ
Polymer
Carlstrom, D.
The crystal structure of α -chitin
J. Biochem Biophys. Cytol., 1957, 3, 669 - 683.
P218.96 35.64 19.50 90˚α-Chitin
Space group
Unit cell dimensions (Bohrradius)
a b c γ
Polymer
Carlstrom, D.
The crystal structure of α -chitin
J. Biochem Biophys. Cytol., 1957, 3, 669 - 683.
What is a-chitin?
Nikolov et al. : Adv. Mater. 22 (2010), 519
67. 66
Hydrogen positions?
H-bonding pattern ?
two conformations
of a-chitin
108 atoms / 52 unknown H-positions
R. Minke and J. Blackwell, J. Mol. Biol. 120, (1978)
What is a-chitin?
68. 67
CPU time Accuracy
•Empirical Potentials
Geometry optimization
Molecular Dynamics
(universal force field)
~10 min
High
Low
~10000 min
~500 min Medium
Resulting
structures
~103
~102
~101
•Tight Binding
(SCC-DFTB)
Geometry optimization
(SPHIngX)
•DFT
(PWs, PBE-GGA)
Geometry Optimization
(SPHIngX)
Hierarchy of theoretical methods
Nikolov et al. : Adv. Mater. 22 (2010), 519
C, C N H
69. rmax = 3.5Å
max = 30°
Hydrogen bond
geometric definition
ground state conformation
1
3
2
4
a [Å] b [Å] c [Å]
PBE - GGA 4.98 19.32 10.45
Exp. [1] 4.74 18.86 10.32
meta-stable conformation
1
3
2
4
5
c
b
H
C
O
N
DFT ground state structure
68Nikolov et al. : Adv. Mater. 22 (2010), 519
70. 69
0.00
0.20
0.40
0.60
0.80
1.00
1.20
-0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02
Lattice elongation [%]
EnergyE-E0[kcal/mol]
a_Lattice
b_Lattice
c_Lattice
c
b
C, C N H
Nikolov et al. : Adv. Mater. 22 (2010), 519
Ab initio prediction of α-chitin elastic properties
74. 73D. Raabe: Advanced Materials 14 (2002) p. 639
Scales in computational crystal plasticity
75. 74
* DFT: density functional theory
Raabe, Sander, Friák, Ma, Neugebauer: Acta Mater. 55 (2007) 4475
From ab-initio to polycrystal mechanics
Gb, Gb2 , ...
<E>
Editor's Notes
Quantitative analysis of the chemical interfaces between austenite and martensite was performed using 1D concentration profiles computed over the region of interest (cylindrical units). We calculated the content of manganese averaged over the 0.5 nm thick cross sections of the cylinders (profile step size 0.5 nm). For both interfaces, strong increase of Mn content up to 26 at. % was observed. The content of the Mn on the austenitic side is about 12 at. %, whereas on the martensitic side a slight depletion of Mn down to 6 at. % can be observed. In order to avoid the contribution of the precipitates to the chemical profile within the martensitic area, we separately measured the 1D concentration profiles within the martensitic matrix after exclusion of the precipitates. These profiles are also plotted.
In order to understand the reasons for the Mn accumulation on the phase boundary, we consider the measured Mn contents. Since the phase equilibrium concentration of Mn in the austenite is much higher than in the ferrite (martensite) as was calculated by using Thermo-Calc (26.7 vs. 3.3 at. %), we expect a redistribution of Mn atoms during aging: enrichment in the austenite and depletion in the martensite. However, the Mn content measured in the austenite remains the same as in the nominal alloy composition (about 12.2 at. %, see Table1). In the martensitic matrix, a slight Mn depletion down to 10.3 at. % was detected. The diffusion in the FCC lattice of austenite is widely suppressed. The martensitic matrix is depleted to 10.3 at. % which is mostly due to the enrichment of Mn in the precipitates. However, Mn content decreases continuously in the martensite toward the phase boundary and, just some nanometers before the Mn-rich layer starts, drops to about 5-6 at. %. The formation of such depletion zone indicates an enhanced diffusion behavior of Mn atoms from the martensite to the austenite. Due to the low diffusion in the austenite, Mn atoms accumulate in the phase boundary and built up a Mn-enriched layer.
The Mn gradient obtained from the thermodynamic calculation using DICTRA provides nearly the same distribution of the Mn content on the austenite/martensite phase boundary (Fig. 4). Enrichment of Mn up to the content of 27 at. % is observed in the interface between austenite and ferrite. For the simulation of the diffusion of Mn in the martensite, we enhanced the mobility of the atoms given for ferrite by a factor of 45.
(During time of annealing at given temperature in (α+γ) range, Mn moves from ferrite to austenite across interface surface between austenite and ferrite until
equilibrium state of the chemical potentials of Mn in austenite and ferrite will be reached. The balance depends on temperature and time of annealing.)
In order to understand the dynamics of the formation of the Mn-enriched layers on the phase boundaries, we consider the phase equilibrium contents of Mn. The averaged content of Mn measured for the Mn-enriched layers is about 26 at. %. This content corresponds to the phase equilibrium content of this element in the austenite which is 26.7 at. %. As known, local phase equilibrium can be easily reached on the grain/phase boundaries. Thus, right on the phase boundary, the equilibrium composition in austenite is reached, and a local phase transformation from martensite to austenite within the Mn-enriched layer can be expected.
However, the
With the growth of the Mn-enriched layer towards the martensitic grain, the material within the layer becomes austenitic and, thus, the phase boundary moves. The final thickness of the Mn-enriched layer is about 20 nm, thus, the phase boundary moved 20 nm during the aging treatment.
The layer-to-austenite interface provides the information about the position of the original phase boundary between the retained austenite and the martensite before aging. Further diffusion of Mn into austenite during aging was suppressed just beyond the crystallographic BCC/FCC boundary. The martensite-to-layer interface, however, indicates the position of the final phase boundary when the Mn diffusion was stopped by the water quenching after the aging treatment. The Mn enriched area in-between these two layers therefore can be addressed as additional austenite formed during the aging.
The growth of the austenite leads to an enhancement of austenite volume fraction during aging. This can be correlated to the growth of the existing austenite grains where the phase boundaries serve as nucleation seeds. We assumed an epitaxial formation of reverted austenite on the phase boundary of the retained austenite.