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A b initio molecular orbital pair potentials for the interaction of Fe2+ and Fe3+ ions with H2O are reported. Molecular dynamics calculations of the static structure of the solvation shell of Fe2+ and Fe3+ in water using the ab initio pair potentials gives physically incorrect results, i.e., the coordination numbers are eight instead of six as observed experimentally. This problem has also been encountered by other workers for divalent transition metal ions in water. By computing three-body energies from the interaction of two water molecules with the cations, we show that the origin of the problem is most likely in the assumption of the additivity of the pair potentials, i.e., neglect of many-body forces. Empirical potentials are reported which take approximate account of the three-body forces and give coordination numbers of six for both Fe2+ and Fe3+ in water.

We have simulated a slab of water with two-dimensional periodic boundary conditions between two metallic walls. The entire compliment of charges, arising from periodic reproductions and from classical images in the metal, are included explicitly by mapping onto a problem with three-dimensional periodicity which is handled by usual Ewald summation methods. Results are presented for charged and uncharged surfaces, permitting an estimate of the differential capacitance arising from the layer of water near the walls. The estimate is about a factor of 2 smaller than the observed differential capacitance of metal–aqueous electrolyte interfaces.

We describe a molecular dynamics model for dissociable, polarizable water. The model, which describes both the static and dynamic properties of real water quite reasonably, contains the following features: Self-consistent local fields are calculated in an extension of an earlier algorithm in which the dipole moments of the water are treated as dynamical variables. An intramolecular three-body potential assures that the molecular properties of water are in agreement with experiment. Ewald methods are used to take account of monopole–dipole and dipole–dipole as well as monopole–monopole interactions. The model was optimized using a Monte Carlo procedure in the parameter space which is described.

The lithium silicates have attracted scientific interest due to their potential use as high-temperature sorbents for CO2 capture. The electronic properties and thermodynamic stabilities of lithium silicates with different Li2O/SiO2 ratios (Li2O, Li8SiO6, Li4SiO4, Li6Si2O7, Li2SiO3, Li2Si2O5, Li2Si3O7, and α-SiO2) have been investigated by combining first-principles density functional theory with lattice phonon dynamics. All these lithium silicates examined are insulators with band-gaps larger than 4.5 eV. By decreasing the Li2O/SiO2 ratio, the first valence bandwidth of the corresponding lithium silicate increases. Additionally, by decreasing the Li2O/SiO2 ratio, the vibrational frequencies of the corresponding lithium silicates shift to higher frequencies. Based on the calculated energetic information, their CO2 absorption capabilities were extensively analyzed through thermodynamic investigations on these absorption reactions. We found that by increasing the Li2O/SiO2 ratio when going from Li2Si3O7 to Li8SiO6, the corresponding lithium silicates have higher CO2 capture capacity, higher turnover temperatures and heats of reaction, and require higher energy inputs for regeneration. Based on our experimentally measured isotherms of the CO2 chemisorption by lithium silicates, we found that the CO2 capture reactions are two-stage processes: (1) a superficial reaction to form the external shell composed of Li2CO3 and a metal oxide or lithium silicate secondary phase and (2) lithium diffusion from bulk to the surface with a simultaneous diffusion of CO2 into the shell to continue the CO2 chemisorption process. The second stage is the rate determining step for the capture process. By changing the mixing ratio of Li2O and SiO2, we can obtain different lithium silicate solids which exhibit different thermodynamic behaviors. Based on our results, three mixing scenarios are discussed to provide general guidelines for designing new CO2 sorbents to fit practical needs.