| 1. |
- Borg, Mikael, et al.
(författare)
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Density of configurational states from first-principles calculations: The phase diagram of Al-Na surface alloys
- 2005
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Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 6:9, s. 1923-1928
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Tidskriftsartikel (refereegranskat)abstract
- The structural phases of AlxNa1-x surface alloys have been investigated theoretically and experimentally. We describe the system using a lattice gas Hamiltonian, determined from density functional theory together with Monte Carlo (MC) calculations. The obtained phase diagram reproduces the experiment on a quantitative level. From calculation of the (configurational) density of states by recently introduced Wang-Landau MC algorithm, we derive thermodynamic quantities such as free energy and entropy which are not directly accessible from conventional MC simulations. We accurately reproduce the stoichiometry, as well as the temperature at which an order-disorder phase transition occurs, and demonstrate the crucial role, and magnitude of the configurational entropy.
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| 2. |
- Borga, M, et al.
(författare)
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Structure and dynamics of Na adsorption on Al(100)
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- The adsorption of 0.2 monolayers (ML) of Na on Al(100) has been studied both experimentally, using low energy electron diffraction (LEED) and high resolution core level spectroscopy (HRCLS), and theoretically, using density functional theory (DFT). Two ordered phases are found: Islands of c (2×2) symmetry with Na atoms occupying four-fold hollow sites result from low temperature deposition and a (√5×√5)R27° structure with Na in surface substitutional sites is formed by annealing of the low temperature island structure at 300 K and subsequent cooling below 230 K. The (√5×√5)R27° structure undergoes a reversible order-disorder phase transition at ~230 K. To investigate this phase transition further, we performed additional DFT calculations for a wide range of coverages (from 0.0625 to 0.5 ML), for adsorption in both hollow and substitutional sites, from which we extract interaction energies which are used in a lattice gas Monte Carlo simulations
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