Extending the domain of quantum mechanical simulations with HPCx: Melting Dario Alfè University...
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![Page 1: Extending the domain of quantum mechanical simulations with HPCx: Melting Dario Alfè University College London.](https://reader035.fdocuments.in/reader035/viewer/2022081603/56649f455503460f94c66897/html5/thumbnails/1.jpg)
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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