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A theoretical study of water equilibria: The cluster distribution versus temperature and pressure for (H2O)n, n=1–60, and ice
Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan. (Beräkningskemi)
Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan. (Beräkningskemi)ORCID-id: 0000-0002-5341-2637
2009 (engelsk)Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, nr 13, s. 134302-134302-13Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The size distribution of water clusters at equilibrium is studied using quantum-chemical calculations in combination with statistical thermodynamics. The necessary energetic data is obtained by quantum-chemical B3LYP computations and through extrapolations from the B3LYP results for the larger clusters. Clusters with up to 60 molecules are included in the equilibrium computations. Populations of different cluster sizes are calculated using both an ideal gas model with noninteracting clusters and a model where a correction for the interaction energy is included analogous to the van der Waals law. In standard vapor the majority of the water molecules are monomers. For the ideal gas model at 1 atm large clusters [56-mer (0–120 K) and 28-mer (100–260 K)] dominate at low temperatures and separate to smaller clusters [21–22-mer (170–280 K) and 4–6-mer (270–320 K) and to monomers (300–350 K)] when the temperature is increased. At lower pressure the transition from clusters to monomers lies at lower temperatures and fewer cluster sizes are formed. The computed size distribution exhibits enhanced peaks for the clusters consisting of 21 and 28 water molecules; these sizes are for protonated water clusters often referred to as magic numbers. If cluster-cluster interactions are included in the model the transition from clusters to monomers is sharper (i.e., occurs over a smaller temperature interval) than when the ideal-gas model is used. Clusters with 20–22 molecules dominate in the liquid region. When a large icelike cluster is included it will dominate for temperatures up to 325 K for the noninteracting clusters model. Thermodynamic properties (Cp, H) were calculated with in general good agreement with experimental values for the solid and gas phase. A formula for the number of H-bond topologies in a given cluster structure is derived. For the 20-mer it is shown that the number of topologies contributes to making the population of dodecahedron-shaped cluster larger than that of a lower-energy fused prism cluster at high temperatures.

sted, utgiver, år, opplag, sider
2009. Vol. 131, nr 13, s. 134302-134302-13
Emneord [en]
water, vapour, ice, quantum chemistry, statistical thermodynamics, hydrogen bonding
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-50778DOI: 10.1063/1.3239474OAI: oai:DiVA.org:liu-50778DiVA, id: diva2:272152
Tilgjengelig fra: 2009-10-14 Laget: 2009-10-14 Sist oppdatert: 2017-12-12
Inngår i avhandling
1. Theoretical Investigations of Water Clusters, Ice Clathrates and Functionalized Nanoparticles
Åpne denne publikasjonen i ny fane eller vindu >>Theoretical Investigations of Water Clusters, Ice Clathrates and Functionalized Nanoparticles
2009 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Nanosized structures are of intermediate size between individual molecules and bulkmaterials which gives them several unique properties. At the same time their relative limitedsizes make them suitable for studies by the methods of computational chemistry. In this thesiswater clusters, ice clathrates and functionalized metal-oxide nanoparticles have been studiedby quantum-chemical calculations and statistical thermodynamics.

The stabilities of water clusters composed of up to 100 molecules have been investigated. Themultitude of possible H-bonded topologies and their importance for determining theproperties of the clusters have been highlighted. Several structural characteristics of thehydrogen bonded network have been examined and the structural factors that determine thestability of an H-bonded network have been identified. The stability of two kinds of oxygenframeworks for water clusters have been analyzed, taking into account thermal energy andentropy corrections. Clusters with many 4-coordinated molecules have been found to be lowerin energy at low temperatures whereas the clusters with less-coordinated molecules dominateat higher temperatures. The equilibrium size distribution of water clusters as a function oftemperature and pressure has been computed using statistical thermodynamics. Themicroscopic local structure of liquid water has been probed by utilizing information from thestudied water clusters. The average number of H-bonds in liquid water has been predicted byfitting calculated average IR spectra for different coordination types in water clusters toexperimental IR spectra.

Water can form an ice-like structure that encloses various molecules such as methane. Thesemethane hydrates are found naturally at the ocean floor and in permafrost regions and canconstitute a large unemployed energy resource as well as a source of an effective green-housegas. The pressure dependencies of the crystal structures, lattice energies and phase transitionsfor the three methane hydrates with the clathrate structures I, II and H have been mapped out.

Zinc oxide is a semiconducting material with interesting luminescence properties that can beutilized in optical devices, such as photodetectors, light emitting devices and biomarkers. Theeffect of water molecules adsorbed on the ZnO surface when adsorbing organic acids havebeen investigated. Changes in optical properties by the adsorption of carboxylic acids havebeen studied and compared with experimental results. Aromatic alcohols at TiO2 metal-oxidenanoparticles have been studied as model systems for dye-sensitizied solar cells. Adsorptiongeometries are predicted and the influence from the adsorbed molecules on the electronicproperties has been studied.

sted, utgiver, år, opplag, sider
Linköping: Linköping University Electronic Press, 2009. s. 52
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1254
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-52746 (URN)978-91-7393-636-1 (ISBN)
Disputas
2009-06-09, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (svensk)
Opponent
Veileder
Tilgjengelig fra: 2010-01-18 Laget: 2010-01-12 Sist oppdatert: 2020-02-19bibliografisk kontrollert

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