1. Extending the domain of quantum mechanical simulations with HPCx: Melting Dario Alfè University College London

2. Why Melting ? The Earth’s core is mainly iron Melting temperature of Fe at ICB Constraint on the temperature of the core

3. Melting Free energy approach Coexistence approach

4. Free energy approach

5. Calculating free energies Thermodynamic integration:

6. Size and k-points tests

7. Lidunka Vočadlo & Dario Alfè, PRB, 65, 214105 (2002)

8. The coexistence approach

9. Density Functional Theory Generalized Gradient Approximation (PW91) VASP code ( Kresse and Furthmuller, PRB 54, 11169 (1996)) USPP (130 eV PW-cutoff) Finite temperature Fermi smearing K-points sampling Efficient charge density extrapolation (Alfe`, Comp. Phys. Comm. 118, 31 (1999)) Ab-initio technical details

10. Scaling tests (Al, 1000 atoms)

11. 512 atoms (  ) (~2 weeks HPCx, 64 PEs) 1000 atoms(  ) (~3 weeks HPCx, 128 PEs)

12. Dario Alfè, Phys. Rev. B, 68, 064423 (2003)

13. 512 atoms (2x2x1) (~4 weeks SUN-SPARC, 16 PEs) 1728 atoms(  ) (~7 months SUN-SPARC, 16 PEs)

15. Conclusions Coexistence of phases for melting is now possible even with first principles techniques (though still very expensive). Next step: Iron ? (One order of magnitude more expensive than Aluminium).