Nuclear quantum effects in electronically adiabatic quantum time correlation functions : Application to the absorption spectrum of a hydrated electron

A general formalism for introducing nuclear quantum effects in the expression of the quantum time correlation function of an operator in a multi-level electronic system is presented in the adiabatic limit. The final formula includes the nuclear quantum time correlation functions of the operator matrix elements, of the energy gap, and their cross terms. These quantities can be inferred and evaluated from their classical analogs obtained by mixed quantum-classical molecular dynamics simulations. The formalism is applied to the absorption spectrum of a hydrated electron, expressed in terms of the time correlation function of the dipole operator in the ground electronic state. We find that both static and dynamic nuclear quantum effects distinctly influence the shape of the absorption spectrum, especially its high-energy tail related to transitions to delocalized electron states. Their inclusion does improve significantly the agreement between theory and experiment for both the low and high frequency edges of the spectrum. It does not appear sufficient, however, to resolve persistent deviations in the slow Lorentzian-like decay part of the spectrum in the intermediate 2-3 eV region

Local structure of liquid/vapour interfaces approaching the critical point

Investigating the structure of fluid interfaces at high temperatures is a particularly delicate task that requires effective ways of discriminating liquid from vapour and identifying the location of the liquid phase boundary, thereby allowing to distinguish intrinsic from capillary fluctuations. Several numerical approaches require introducing a coarse-graining length scale, often heuristically chosen to be the molecular size, to determine the location of the liquid phase boundary. Here, we propose an alternative rationale for choosing this coarse-graining length scale; we require the average position of the local liquid phase dividing surface to match its flat, macroscopic counterpart. We show that this approach provides additional insight into the structure of the liquid/vapour interface, suggesting the presence of another length scale beyond the bulk correlation one that plays an important role in determining the interface structure

What does an ionic liquid surface really look like? Unprecedented details from molecular simulations

We present the first intrinsic analysis of the surface of the [bmim][PF6] room-temperature ionic liquid. Our detailed analysis reveals unprecedented details about the structure of the interface by providing the relative prevalence of different molecular orientations. These results suggest that experimental data should be reinterpreted considering a distribution of molecular arrangements

Polarization effects at the surface of aqueous alkali halide solutions

The polarizability of ions, with its strong influence on their surface affinity, is one of the crucial pieces of the complex puzzle that determines the surface properties of electrolyte solutions. Here, we investigate the electrical and structural properties of alkali halide solutions at a concentration of about 1.3 M using molecular dynamics simulations of polarizable water and ions models. We show that capillary fluctuations have a dramatic impact on the sampled quantities and that without removing their smearing effect, it would be impossible to resolve the local structure of the interfacial region. This procedure allows us to investigate in detail the dependence of the permanent and induced dipoles on the distance from the interface. The enhanced resolution gives us access to the surface charges, estimated using the Gouy-Chapman theory, despite the Debye length being shorter than the amplitude of capillary fluctuations

Gestational Diabetes amongst Immigrant women

Bacheloroppgave sykepleie, 2014Som følge av innvandring er Norge blitt et kulturelt mer mangfoldig samfunn. Dette fører til noen utfordringer for helsepersonell som møter personer med en annen kulturell bakgrunn. Denne bacheloroppgavens tema er svangerskapsdiabetes hos kvinner med innvandrerbakgrunn. Den setter søkelys på veiledning til innvandrerkvinner, slik at de kan forebygge komplikasjoner under svangerskapet eller utvikling diabetes type 2 senere. Det er sykepleierens helsefremmende- og forebyggende funksjon som er sentralt i oppgaven. For å sikre at kvinnene opparbeider seg gode mestringsstrategier, må sykepleiere ta hensyn til deres kulturelle og religiøse bakgrunn. Sykepleiere må kartlegge innvandrerkvinnenes deltakerforutsetninger og rammefaktorer i forbindelse med veiledningen. Dette dreier seg om språkbakgrunn og pårørendes rolle knyttet til kvinnenes mestringsmuligheter av sin tilstand. Bacheloroppgaven tar utgangspunkt i Benner og Wrubels sykepleieteori om mestring av sykdom. Deres fokus på viktigheten av å vektlegge pasienters subjektive forutsetninger og kulturelle bakgrunn har vært retningsgivende for å belyse oppgavens problemstilling

Fracture Properties of Kerogen and Importance for Organic-Rich Shales

International audienceOil and gas produced from organic-rich shales have become in the last ten years one of the most promising sources of unconventional fossil fuels. The oil and gas are trapped in rocks of very small permeability, but hydraulic fracturing enables to operate those reservoirs with competitive costs. The global reserves of shale oil and gas that are potentially recoverable are equivalent to tens of years of world con- sumption. However, hydraulic fracturing is facing many challenges regarding the productivity but also the security and the environment. One of those challenges is to un- derstand how the fractures propagate underground. The propagation depends on the mechanical stress prevailing in the reservoir and on the fracture properties of the rocks. Regarding the fracture properties, the oil and gas indus- try developed brittleness indicators to distinguish between brittle rocks (containing mostly calcite and silica) and duc- tile rocks (containing a significant proportion of clay and kerogen). During fracturing, a brittle rock shatters easily leading to a well-distributed network of fractures, whereas a ductile rock deforms instead of shattering leading to few fractures and in some situations acting as a barrier to the fracture propagation. In this work, we study the role of kerogen in the ductility of shale. The ultimate objective is to develop a fine understanding of the fracture properties of shales

A systematic molecular simulation study of ionic liquid surfaces using intrinsic analysis methods

In this paper, we apply novel intrinsic analysis methods, coupled with bivariate orientation analysis, to obtain a detailed picture of the molecular-level structure of ionic liquid surfaces. We observe pronounced layering at the interface, alternating non-polar with ionic regions. The outermost regions of the surface are populated by alkyl chains, which are followed by a dense and tightly packed layer formed of oppositely charged ionic moieties. We then systematically change the cation chain length, the anion size, the temperature and the molecular model, to examine the effect of each of these parameters on the interfacial structure. Increasing the cation chain length promotes orientations in which the chain is pointing into the vapor, thus increasing the coverage of the surface with alkyl groups. Larger anions promote a disruption of the dense ionic layer, increasing the orientational freedom of cations and increasing the amount of free space. The temperature had a relatively small effect on the surface structure, while the effect of the choice of molecular model was clearly significant, particularly on the orientational preferences at the interface. Our study demonstrates the usefulness of molecular simulation methods in the design of ionic liquids to suit particular applications

The intrinsic structure of the interface of partially miscible fluids : an application to ionic liquids

We investigate by means of Molecular Dynamics simulations how the intrinsic sur- face structure of liquid/liquid interfaces involving ionic liquids depends on the opposite phase of varying polarity. We study 1-n-butyl-3-methylimidazolium hexa uorophos- phate (BMIM PF 6 ) and 1-n-butyl-3-methylimidazolium bis(tri uoromethylsulfonyl)imid (BMIM NTf 2 ). The opposite phase is either cyclohexane or water, but as a reference, IL { vacuum interfaces are also studied. We combine a distance-based cluster search algorithm with the ITIM intrinsic analyzing method to separate liquid phases showing non-negligible mutual miscibility and to identify atoms residing at the instantaneous surface. In contrast to the well structured surface of IL { vacuum systems, at liq- uid/liquid interfaces of ILs density correlations, ionic associations and orientational preferences are all weakened, this eect being much more pronounced when the other species is water. In such systems we observe a drastic reduction in the presence of the cation at the surface and an increase of appearance of polar moieties (of both the cations and anions) leading to decreased apolar character of the interface. Furthermore, cations are mostly found to turn with their butyl chains toward the bulk while having their methyl groups sticking towards water. Anion-cation associations are reduced and partially replaced by water-anion and rarely also water-cation associations

Stability of the high-density Jagla liquid in 2D : sensitivity to parameterisation

We computed the pressure-temperature phase diagram of the hard-core two-scale ramp potential in two-dimensions, with the parameterisation originally suggested by Jagla[E. A. Jagla, Phys. Rev. E 63, 061501 (2001)], as well as with a series of systematically modified variants of the model to reveal the sensitivity of the stability of phases. The nested sampling method was used to explore the potential energy landscape, allowing the identification of thermodynamically relevant phases, such as low- and high-density liquids and various crystalline forms, some of which have not been reported before. We also proposed a smooth version of the potential, which is differentiable beyond the hard-core. This potential reproduces the density anomaly, but forms a dodecahedral quasi-crystal structure at high pressure. Our results allow to hypothesise on the necessary modifications of the original model in order to improve the stability of the metastable high density liquid phase in 3D