extending the domain of quantum mechanical simulations with hpcx: melting
DESCRIPTION
Extending the domain of quantum mechanical simulations with HPCx: Melting. Dario Alf è University College London. Why Melting ?. The Earth’s core is mainly iron Melting temperature of Fe at ICB Constraint on the temperature of the core. Melting. Free energy approach. Coexistence approach. - PowerPoint PPT PresentationTRANSCRIPT
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Extending the domain of quantum mechanical simulations
with HPCx: Melting
Dario AlfèUniversity College London
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Why Melting ?
• The Earth’s core is mainly iron
• Melting temperature of Fe at ICB
• Constraint on the temperature of the core
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Melting
Free energy approach
Coexistence approach
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Free energy approach
liquid solidG (P,T) G (P,T)
T 100 K G 10 meV/atom
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Calculating free energies
Thermodynamic integration:
1
ref ref
0
F F d U U
λ refU (1 λ)U λU
BU(R)/ TB 3N
V
1F(V,T) T ln dR e
N!kk
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Size and k-points tests
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Lidunka Vočadlo & Dario Alfè, PRB, 65, 214105 (2002)
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The coexistence approach
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• 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
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Scaling tests (Al, 1000 atoms)
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512 atoms ()(~2 weeks HPCx, 64 PEs)
1000 atoms()(~3 weeks HPCx, 128 PEs)
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Dario Alfè, Phys. Rev. B, 68, 064423 (2003)
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512 atoms (2x2x1)(~4 weeks SUN-SPARC, 16 PEs)
1728 atoms()(~7 months SUN-SPARC, 16 PEs)
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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).
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