Modelling structure, dynamics, and vibrational spectroscopy of simple oxides under pressure

1. Modelling structure, dynamics, and vibrational spectroscopy of simple oxides under pressure 1000 Km ! Gyrs !! mm / yr !!! Sandro Scandolo (the Abdus Salam ICTP, Trieste, Italy)

3. Outline Interatomic potentials accurate potentials from fitting to ab-initio trajectories Compressing SiO2 glass densified glass, phase transitions, etc Rheology of MgO calculating the critical shear stress for dislocation flow Raman and Infrared spectra for silica polymorhps without empirical parameters

4. Outline Interatomic potentials accurate potentials from fitting to ab-initio trajectories Compressing SiO2 glass densified glass, phase transitions, etc Rheology of MgO calculating the critical shear stress for dislocation flow Raman and Infrared spectra for silica polymorhps without empirical parameters

5. Ab-initio Molecular Dynamics Charge-transfer models (Goddard III et al.) Distortable ion models (Madden et al.) Potential induced breathing Variational induced breathing (Cohen et al.) Rigid ion models

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

7. New polarizable potential For SiO2: P. Tangney and S. Scandolo JCP 117, 8898 (2002) See also: D. Herzbach, K. Binder, M. Muser, JCP (2005)

8. Outline Interatomic potentials accurate potentials from fitting to ab-initio trajectories Compressing SiO2 glass densified glass, phase transitions, etc Rheology of MgO calculating the critical shear stress for dislocation flow Raman and Infrared spectra for silica polymorhps without empirical parameters

9. Is there a first-order phase transition in compressed glass? Why can silica glass be permanently densified? Complexity of (crystal) phase diagram supports this notion Molecular dynamics says YES: D. Lack, PRL 84 (2000) 4629 Some experiments say YES Mukherjee et al, PRL 87 (2001) 195501 Other experiments say NO Inamura et al.,PRL 93(2004) 015501 Inamura et al.,PRL 93(2004) 015501

10. X-ray structure factor of compressed glass Y. Liang, C.Miranda, and S. Scandolo Exp: Inamura et al.,PRL 93(2004) 015501

11. Hysteresis between 0 and 10 GPa Y. Liang, C.Miranda, and S. Scandolo Exp: Meade and Jeanloz

12. Si-O coordination number in the glass Y. Liang, C.Miranda, and S. Scandolo Higher diffusion Lower strenght Tetrahedral network

13. “Strength“ of compressed glass Strength Y. Liang, C.Miranda, and S. Scandolo

14. Anomalous compressibility not due to a phase transition Y. Liang, C.Miranda, and S. Scandolo

15. Outline Interatomic potentials accurate potentials from fitting to ab-initio trajectories Compressing SiO2 glass densified glass, phase transitions, etc Rheology of MgO calculating the critical shear stress for dislocation flow Raman and Infrared spectra for silica polymorhps without empirical parameters

16. Critical Resolved Shear Stress in MgO Seismic anomalies in the lower mantle attributed to partial orientation of crystals. Partial orientation is determined by differences in the CRSS between different crystallographic planes.

17. A Distortable ion model Tangney and Scandolo, J. Chem. Phys., 2003 s Environment-dependent membrane L R

18. Solid MgO: Phonons

19. MgO: equations of state

20. Slip plane This work (GPa) expt (GPa) 0.066 0.06 3.54 > 1.1 2.76 ~2.6 Critical Resolved Shear Stress at P = 0 GPa C. Miranda and S. Scandolo, Comp. Phys. Comm. (2005)

21. may not be the dominant slip system at geophysical conditions Critical resolved shear stress: pressure dependence ? C. Miranda and S. Scandolo, to be published

22. Outline Interatomic potentials accurate potentials from fitting to ab-initio trajectories Compressing SiO2 glass densified glass, phase transitions, etc Rheology of MgO calculating the critical shear stress for dislocation flow Raman and Infrared spectra for silica polymorhps without empirical parameters

23. Infrared spectra of cristobalite a-cristobalite b-cristobalite Y. Liang, C.R. Miranda, S. Scandolo, to be published

24. Raman spectra of quartz a-quartz b-quartz Y. Liang, C.R. Miranda, S. Scandolo, to be published

25. Raman spectra of cristobalite a-cristobalite b-cristobalite Y. Liang, C.R. Miranda, S. Scandolo, to be published

26. Prospects Interatomic potentials for ternary systems (e.g. MgSiO3) Thermal conductivity Rheology of perovskite / post perovskite

27. Thanks to Paul Tangney (now at UC Berkeley) Caetano Miranda (ICTP, soon at MIT) Yunfeng Liang (SISSA)