The 6th School on Simulation and Modeling Physics "Ab-initio methods and their applications"
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Transcript of The 6th School on Simulation and Modeling Physics "Ab-initio methods and their applications"
Tue.27 Nov. Wed.28 Nov. Thu.29 Nov.
8h30 - 9h45Topical lecture
Planets / High PressureTopical lecture
Atmospheric physics
Methods: Ab-initio Molecular
Dynamics
9h45 - 10h15 Coffee break
10h15 -11h30Methods
Plane waves, cut-off, k-points, pseudopotentials, DFT, etc
Seminars Computer Lab 3
11h30 – 13h30 Lunch time
13h30 – 16h00 Computer Lab 1 Computer Lab 2 Computer Lab 4
The 6th School on Simulation and Modeling Physics"Ab-initio methods and their applications" Hanoi, 27 - 29 November 2007
Exploring planetary interiors by ab-initio molecular dynamics
6th SMP, Hanoi, Nov 27-29, 2007
Sandro Scandolo(the Abdus Salam ICTP, Trieste, Italy)
The Abdus Salam International Centre for Theoretical Physics(under UNESCO / IAEA), Trieste, Italy
ICTP’s mission:
To foster the growth of advanced studies and research in physics and mathematics, especially among researchers from developing countries
Opportunities
- Conferences / Schools throughout the year
- Associates (our faculty “in the field”)
- Visitors (junior, STEP, TRIL, etc)
- Diploma Course
www.ictp.it
Materials SciencePlanetary Science
High pressure in
1951: the first man-made diamonds
1991: Earth’s core conditionsreproduced in the laboratory
Shock waves Diamond anvil cell
Approximations
- Born-Oppenheimer - Classical nuclei- Density functional theory
from “first principles”
Variable-cell molecular dynamics
[Parrinello & Rahman, 1981]
Outline
High Pressure in Materials Science:
+ “Carbonia”: a silica-like CO2 amorph+ Novel transition metal nitrides
High pressure in Planetary Science:
+ Carbon in planetary interiors+ Melting of iron
Silica-like CO2 : the crystal phases
+ Molecular CO2 predicted to tranform into a silica-like crystal at high pressure
+ Silica-like phases of CO2 predicted to be ultrahard
Molecular CO2 Candidate theoretical structures for silica-like CO2
Serra, Cavazzoni, Chiarotti, Scandolo, Tosatti, Science 284, 788 (1999)
Crystal structure of silica-like CO2
not yet determined
Is there a glass analog?
Experimental confirmation of silica-like CO2
Yoo et al, Science 283, 1510 (1999)
“Carbonia”: the silica-like CO2 glass
Experimental evidence for amorphous CO2
Santoro, Gorelli, Bini, Ruocco, Scandolo, Crichton,Nature, in press (2006)
Compression by ab-initio molecular dynamics gives:
At 1000 K and 100 GPa: a crystalline phase
At 2000 K and 80 GPa: an amorphous phase
Octahedral CO6Tetrahedral CO4
Platinum nitride: PtN or PtN2?
Raman shift (cm-1)
Gregoryanz et al, Nature Mat. (2004)Crowhurst et al, Science (2006)
Ab-initio calculations on structures with 1:1 stoichiometry fail to reproduce the experimentalRaman spectra
Single-bonded polymeric nitrogen
Eremets et al, Nature Mat. (2004)
Molecular N2
Polymeric N
Platinum nitride: PtN2 pyriteYoung, Montoya, Lazzeri, Sanloup, Gregoryanz, Scandolo, PRB 2006
Raman spectra
X-ray diffraction
MN2 with interstitial N2 units: a new class of transition metal nitrides?
Young, Sanloup, Gregoryanz, Scandolo, Hemley, Mao, PRL 96, 155501 (2006)
IrN2
Single bonded N-N
PtN2 pyrite
New “heavy” metal nitrides are superhard
Bulk modulus: 428 GPa (IrN2), 358 GPa (OsN2)
H2O+CH4+NH3
Marvin Ross, “Diamonds in the sky”Nature (1981)
Methane was found to dissociate under a shock wave
Scandolo & Jeanloz, American Scientist (2003)
Methane dissociation: what do simulations say
F. Ancilotto et al., Science 275, 1288 (1997)
Compressed methane Compressed methaneheated up to 4000 K
Before compression After compression
Methane dissociation: the experimental confirmationL.R. Benedetti et al., Science 283, 100 (1999)
Melting of Carbon
diamond liquid
BC8, SC ??
Neptune and Uranus isentrope
X. Wang, S. Scandolo, R. Car, Phys. Rev. Lett 2005
3.8
4.3
4.7
5.2
5.3-5.8
Coordination number
Accuracy of DFT?: Melting of silicon
Solid
Liquid
Tm(LDA) = 1380 KTm(GGA) = 1520 KTm(meta-GGA) = 1700 K
Tm(experiment) = 1687 K
X. Wang, S. Scandolo, R. Car
How hot is the centre of the Earth?
liqui
dso
lid
Inner core (solid Fe) Outer core
(liquid Fe)
Mantle
The temperature at the inner core boundary coincides with the melting temperature of Fe at 330 GPa
The “optimized” potential method
“Optimized” potential at P,T
A. Laio et al, Science 287, 1027 (2000)
Melting of Iron at Earth’s core pressures
Inner-Outer core boundary
A. Laio et al, Science 287, 1027 (2000)
Our results
Shock waveexperiments
Static experiments
DFT-basedcalculation byAlfe’ et al
D. Stevenson, Nature 423, 239 (2003)
The crew:J. MontoyaA. YoungR. RousseauC. CavazzoniY. LiangX. WangA. LaioR. Car….www.quantum-espresso.org