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dc.contributor.advisorNicola Marzari.en_US
dc.contributor.authorSit, Patrick Hoi Landen_US
dc.contributor.otherMassachusetts Institute of Technology. Dept. of Physics.en_US
dc.date.accessioned2007-11-16T14:24:37Z
dc.date.available2007-11-16T14:24:37Z
dc.date.copyright2006en_US
dc.date.issued2006en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/39561
dc.descriptionThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.en_US
dc.descriptionIncludes bibliographical references (p. 127-141).en_US
dc.description.abstractIn this thesis, we show for the first time how it is possible to calculated fully from first-principles the diabatic free-energy surfaces of electron-transfer reactions. The excitation energy corresponding to the transfer of an electron at any given ionic configuration (the Marcus energy gap) is accurately assessed within ground-state density-functional theory via a novel penalty functional for oxidation-reduction reactions that appropriately acts on the electronic degrees of freedom alone. The self-interaction error intrinsic to common exchange-correlation functionals is also corrected by the same penalty functional. The diabatic free-energy surfaces are then constructed from umbrella sampling on large ensembles of configurations. As a paradigmatic case study, the self-exchange reaction between ferrous and ferric ions in water is studied in detail. Since the solvent plays an central role in mediating the process, studying electron-transfer reactions requires us to first understand the structure and dynamics of the solvent molecules (water molecules in our case). Therefore, we have also studied the static and dynamical properties of (heavy) water at ambient conditions with extensive first-principles molecular-dynamics simulations in the canonical ensemble, with temperatures ranging between 325 K and 400 K.en_US
dc.description.abstract(cont.) Density-functional theory, paired with a modern exchange-correlation functional (PBE), provides an excellent agreement for the structural properties and binding energy of the water monomer and dimer. On the other hand, contrary to a long-standing belief, the structural and dynamical properties of the bulk liquid show a clear enhancement of the local structure compared to experimental results; a distinctive transition to liquid-like diffusion occurs in the simulations only at the elevated temperature of 400 K. The local coordination and structure of water is still a very debated matter and in collaboration with experimentalists at the European Synchrotron Radiation Facility in Grenoble, we have characterized the structure and the local environment in water with a combination of inelastic X-ray scattering and first-principles calculations, under conditions ranging from the normal state to the supercritical regime. The same temperature dependence of the Compton profile is observed in experiment and simulation. A well-defined linear correlation is identified between Compton profile differences and changes in the number of hydrogen bonds per molecule, that is consistent with well-established structural models, and that confirms the prevailing picture of hydrogen bonding under normal conditions.en_US
dc.description.abstract(cont.) While close to the critical point we observe a clear signature of density fluctuations, supercritical water is characterized by a sharp increase in under-coordinated clusters, with a significant number of dimers and trimers. Last, we implemented a Hubbard U correction in our first-principles molecular dynamics to improve the hybridization between a transition metal ion and its surroundings. The implementation has been tested for ferrous and ferric ions solvation in water. The effects of the Hubbard U correction on the electron-transfer reaction is also studied.en_US
dc.description.statementofresponsibilityby Patrick Hoi Land Sit.en_US
dc.format.extent141 p.en_US
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582
dc.subjectPhysics.en_US
dc.titleAqueous systems from first-principles : structure, dynamics and electron-transfer reactionsen_US
dc.typeThesisen_US
dc.description.degreePh.D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Physics
dc.identifier.oclc174146642en_US


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