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