Ab-initio simulations of matter at extreme conditions: a window into the centers of planets

1. Ab-initio simulations of matter at extreme conditions: a window into the centers of planets Sandro Scandolo (ICTP, Trieste, Italy) Joint ICTP-TWAS CaribbeanSchool 2012

2. Scandolo & Jeanloz, American Scientist 2003 Scandolo & Jeanloz, American Scientist (2003)

3. Scandolo & Jeanloz, American Scientist (2003)

4. Diamond Graphite

5. High pressure in Physics Materials Science Planetary Science 1991: Earth’s core conditions reproduced in the laboratory 1935: prediction of metallic hydrogen 1951: the first man- made diamonds

6. Shock waves Diamond anvil cell

7. Scandolo & Jeanloz, American Scientist (2003)

8. Quantum simulations: The “standard model” “Molecular dynamics” for atoms Ma = F = -dE/dR Schroedinger equation for electrons Hy = Ey R. Cohen Electron charge density in SiO2 stishovite “Ab-initio” molecular dynamics = Classical molecular dynamics in the potential energy surface generated by the electrons in their quantum ground state

10. Water and methane at planetary conditions

11. 60% molar fraction

12. phase diagram of water from first principles C. Cavazzoni et al., Science 283, 44 (1999) Experimental confirmation (?) of superionic phase: A. Goncharov et al., Phys. Rev. Lett. (2006)

13. C. Cavazzoni et al., Science 283, 44 (1999) Superionic Water P = 150 GPa T = 2500 K Proton diffusion by hopping Oxygen sublattice remains crystalline

14. Scandolo & Jeanloz, American Scientist (2003) H2O+CH4+NH3 Marvin Ross, “Diamonds in the sky” Nature (1981) Methane was found to dissociate under a shock wave

15. Dissociation of methane at extreme (planetary) conditions F. Ancilotto et al., Science 275, 1288 (1997) Compressed methane after heating to 4000 K Compressed methane L.R. Benedetti et al., Science 283, 100 (1999)

16. 92% molar fraction

17. CH4 / H2O mixtures at extreme conditions 92% of the Uranus and Neptune ice layer Fluid inclusions, abiogenic formation of methane Prototype of hydrophobic interactions How corrosive is ionized water? Methane hydrate clathrates SIMULATIONS: 26 CH4 + 38 H2O at 4 different P-T

18. Methane / water mixture at 50 GPa Fast proton diffusion by proton hopping between adjacent molecules Methane “attacked” by ionized water Occasional formation of C-O bonds No formation of longer hydrocarbons (C-C bonds) M.-S. Lee and S. Scandolo, Nature Comm. 2011

20. >90% molar fraction

21. E. Wigner and H.B. Huntington “On the possibility of a metallic modification of hydrogen” J. Chem. Phys. 3, 764 (1935) Hemley and Mao, Rev Mod Phys

22. ?

23. ? • At which depth does hydrogen become an electrical conductor? • Is metallization accompanied by a sharp density change?

24. Molecular to non-molecular transition S. Scandolo, Proc. Natl. Acad. Sci. USA, 2003

25. Down to Earth…

26. How hot is the centre of the Earth? liquid solid The temperature at the inner core boundary coincides with the melting temperature of Fe at 330 GPa Inner core (solid Fe) Mantle Outer core (liquid Fe)

27. A number of mineral physics phenomena are difficult to address or even beyond reach for first-principles simulations, because of time scale and size limitations. Examples include thermal conductivity highly viscous silicate melts melting temperatures (some aspects of) rheological properties at high T etc…

29. The “optimized” potential method “Optimized” potential at P,T A. Laio et al, Science 287, 1027 (2000)

30. P. Tangney and S. Scandolo JCP 117, 8898 (2002)

31. How hot is the Earth’s core? A. Laio et al, Science 287, 1027 (2000) Shock wave experiments DFT-based calculation by Alfe’ et al Liquid Fe Our results Inner-Outer core boundary Static experiments Solid Fe

33. D. Stevenson, Nature 423, 239 (2003)

34. Thanks to: M.-S. Lee M. Fontana L. Giacomazzi J. Christie Y. Liang ICTP A. Young A. Hernandez Nieves J. Montoya R. Rousseau C. Miranda P. Tangney A. Laio S. Serra E. Tosatti SISSA F. Tassone G. Profeta L’Aquila R. Car X. Wang Princeton ...and a countless number of experimentalists...