8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P1.12Fri 911:10-14:00An efficient method of calculating free energies ofcharged systemsRobert Horton, 1 Mike Finnis, 1 George Jackson, 1 Amparo Galindo, 1 and AndrewHaslam 11 Imperial College London, South Kensington Campus, SW7 2AZ, London, UnitedKingdomCharged particles play a vital role in lattice gas models and solid-state chemistry, becausevacancies and interstitials in the underlying lattice may transport both charge and matter bya process of diffusion under a gradient of electrochemical potential. The free energy of suchsystems is often described with the ideal solution model, even though the concentrations of suchdefects may be very high (∼ 10%), as in the doped materials used in solid oxide fuel cells, wherethe treatment of point defects as a dilute solution is inadequate. Traditional molecular simulationmethods have been employed in order to calculate free energies of these systems, however due tothe long ranged nature of the interactions such simulations are computationally expensive. Wehave applied the Wang-Landau Monte Carlo method [1, 2] to simple charged systems, wherethe interaction between charges is described by Ewald summation, and compared it with moretraditional approaches (such as Metropolis Monte Carlo). The method has been further developedto reduce computational cost for systems of interacting charges on a lattice. As one obtains thefull density of states of the system in a single calculation with the Wang-Landau method, it allowsthe free energies of the system to be calculated at any desired temperature at negligible extracost. A rapidly convergent density of states was obtained by generating its moments during theWang-Landau iterations, and then applying the method of maximum entropy (MAXENT) [3].[1] F. Wang and D. P. Landau, Phys. Rev. Lett. 86, 10 (2000).[2] F. Wang and D. P. Landau, Phys. Rev. E 64, 056101 (2001).[3] Mead L R and Papanicolaou N, J. Math. Phys. 25 2404-177 (1984).12