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Figure 1.
The computer time, in seconds, required for a time step in Quantum Monte Carlo using either
extended orbitals taken from a density functional theory (DFT) calculation, using these
orbitals after they have been transformed into localized orthogonal Wannier orbitals, or
after they have been transformed into localized non-orthogonal orbitals versus the number
of electrons in the system. These orbitals occur in the determinants of the many-body trial function.
With extended orbitals the computer time scales as the cube of the number of electrons,
while with localized orbitals the computer time scales linearly with the number of electrons.
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Quantum Monte Carlo Assessment of the Relevance of Electronic Correlations
on the Defect Formation Energies and Equation of State of Metals
Andrew Williamson,
Randolph Hood, Jonathan DuBois,
John Pask, Baback Sadigh, and Fernando Reboredo (Oak Ridge National Laboratory)
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In this project we are developing a highly accurate, first principles
computational capability to calculate defect formation energies and
the equation of state (EOS) of metallic systems. We are using a newly
developed algorithm that enables the study of metallic systems with
quantum Monte Carlo (QMC) methods. To date, technical limitations have
restricted the application of QMC methods to semiconductors, insulators
and the homogeneous electron gas. Using a new formulation based on
optimized, non-orthogonal orbitals we have overcome these limitations.[1,2]
Using this new "QMC for metals" approach we are determining, for the first
time, the significance of correlation effects in the EOS and in the
formation energies of point defects, impurities, surfaces and interfaces
in metallic systems. These calculations go beyond the state-of-the-art
accuracy which is currently obtained with Density Functional Theory (DFT)
approaches. These benchmark calculations will provide more accurate
predictions for the EOS and the formation energies of vacancies and
interstitials in simple metals. These are important parameters in
determining the mechanical properties as well as the micro-structural
evolution of metals in irradiated materials or under extreme conditions.
Furthermore, we plan to study, for the first time, electron correlations
in a model system close to the metal-insulator transition point with a
parameter-free theory.
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REFERENCES
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A.J. Williamson, R.Q. Hood, and J.C. Grossman
Linear-Scaling
Quantum Monte Carlo Calculations,
Phys. Rev. Lett. 87, 246406 (2001).
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F. A. Reboredo and A. J. Williamson,
Optimized nonorthogonal
localized orbitals for linear scaling quantum Monte Carlo calculations,
Phys. Rev. B 71, 121105 (2005).
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EOS & MT
| Condensed Matter Physics
| Physics & Adv. Tech.
| LLNL
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Maintained by Robert E. Rudd -- Last updated on 10 March 2007.
UCRL-WEB-229431
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