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) Seminario Galileiano, Pisa 29/04/2010

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 e--e- interactions: Density Functional Theory e--nuclei interactions: Pseudopotentials 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

9. Asian-Pacific School, Beijing, July 2004 Quantum ESPRESSO is an open-source suite of computer codes for electronic-structure calculations and materials modeling. It is based on density-functional theory, plane waves, and pseudopotentials. Features include: structural optimizations, dielectric and Raman tensors phonons infrared spectra elastic constants NMR spectra ab-initio molecular dynamics etc… “First-principles codes for computational crystallography in the Quantum-ESPRESSO package” S. Scandolo et al., Z. Kristallogr. 220, 574 (2005) www.quantum-espresso.org

11. Water and methane at planetary conditions

12. 60% molar fraction

13. 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)

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

15. 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

16. 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)

17. 92% molar fraction

18. 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

19. CH4 / H2O mixtures at extreme conditions Choice of P-T points on the water phase diagram CH4 / H2O

20. CH4 / H2O mixtures at extreme conditions Radial distribution functions

21. CH4 / H2O mixtures at extreme conditions Softening of the C—O intermolecular potential

22. Maximally localized molecular orbitals (Wannier functions) CH4 / H2O mixtures at extreme conditions Distortion of CH4 at 15 GPa C...O distance about 3 A C-H bond becomes more ionic with increasing pressure Increased ionicity and thermal disorder cause CH4 to acquire a significant instantaneous dipole moment (about 0.5 D at 15 GPa) M.-S. Lee and S. Scandolo, in preparation

23. 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, In preparation

24. CH4 / H2O mixtures at extreme conditions Metallic behavior at milder conditions than pure water

26. >90% molar fraction

27. 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

28. ?

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

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

31. Is there a first-order phase transition inside Jupiter/Saturn? S. Scandolo, Proc. Natl. Acad. Sci. USA, 2003 Jupiter/Saturn isentrope

32. Down to Earth…

33. 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)

34. 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…

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

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

38. 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

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

41. 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...