Renormalization of Optical Excitations in Molecules near a Metal Surface

The lowest electronic excitations of benzene and a set of donor-acceptor molecular complexes are calculated for the gas phase and on the Al(111) surface using the many-body Bethe-Salpeter equation (BSE). The energy of the charge-transfer excitations obtained for the gas phase complexes are found to be around 10% lower than the experimental values. When the molecules are placed outside the surface, the enhanced screening from the metal reduces the exciton binding energies by several eVs and the transition energies by up to 1 eV depending on the size of the transition-generated dipole. As a striking consequence we find that close to the metal surface the optical gap of benzene can exceed its quasiparticle gap. A classical image charge model for the screened Coulomb interaction can account for all these effects which, on the other hand, are completely missed by standard time-dependent density functional theory.Comment: 4 pages, 3 figures; revised versio

Benchmarking GW against exact diagonalization for semi-empirical models

We calculate groundstate total energies and single-particle excitation energies of seven pi conjugated molecules described with the semi-empirical Pariser-Parr-Pople (PPP) model using self-consistent many-body perturbation theory at the GW level and exact diagonalization. For the total energies GW captures around 65% of the groundstate correlation energy. The lowest lying excitations are overscreened by GW leading to an underestimation of electron affinities and ionization potentials by approximately 0.15 eV corresponding to 2.5%. One-shot G_0W_0 calculations starting from Hartree-Fock reduce the screening and improve the low-lying excitation energies. The effect of the GW self-energy on the molecular excitation energies is shown to be similar to the inclusion of final state relaxations in Hartree-Fock theory. We discuss the break down of the GW approximation in systems with short range interactions (Hubbard models) where correlation effects dominate over screening/relaxation effects. Finally we illustrate the important role of the derivative discontinuity of the true exchange-correlation functional by computing the exact Kohn-Sham levels of benzene.Comment: 9 pages, 5 figures, accepted for publication in Phys. Rev.

'Rapid fire' spectroscopy of Kepler solar-like oscillators

The NASA Kepler mission has been continuously monitoring the same field of the sky since the successful launch in March 2009, providing high-quality stellar lightcurves that are excellent data for asteroseismology, far superior to any other observations available at the present. In order to make a meaningful analysis and interpretation of the asteroseismic data, accurate fundamental parameters for the observed stars are needed. The currently available parameters are quite uncertain as illustrated by e.g. Thygesen et al. (A&A 543, A160, 2012), who found deviations as extreme as 2.0 dex in [Fe/H] and log g, compared to catalogue values. Thus, additional follow-up observations for these targets are needed in order to put firm limits on the parameter space investigated by the asteroseismic modellers. Here, we propose a metod for deriving accurate metallicities of main sequence and subgiant solar-like oscillators from medium resolution spectra with a moderate S/N. The method takes advantage of the additional constraints on the fundamental parameters, available from asteroseismology and multi-color photometry. The approach enables us to reduce the analysis overhead significantly when doing spectral synthesis, which in turn will increases the efficiency of follow-up observations.Comment: 3 pages, 2 figures. Proceedings from Asteroseismology of Stellar Populations in the Milky Way 2013 to appear in 'Astrophysics and Space Science Proceedings

The age of 47Tuc from self-consistent isochrone fits to colour-magnitude diagrams and the eclipsing member V69

Our aim is to derive a self-consistent age, distance and composition for the globular cluster $47\,$Tucanae ($47\,$Tuc; NGC104). First, we reevaluate the reddening towards the cluster resulting in a nominal $E(B-V)=0.03\pm0.01$ as the best estimate. The $T_{\rm eff}$ of the components of the eclipsing binary member V69 is found to be $5900\pm72$ K from both photometric and spectroscopic evidence. This yields a true distance modulus $(m-M)_0=13.21\pm0.06$(random)$\pm0.03$(systematic) to $47\,$Tuc when combined with existing measurements of V69 radii and luminosity ratio. We then present a new completely self-consistent isochrone fitting method to ground based and $\textit{HST}$ cluster colour-magnitude diagrams and the eclipsing binary member V69. The analysis suggests that the composition of V69, and by extension one of the populations of $47\,$Tuc, is given by [Fe/H]$\sim-0.70$, [O/Fe]$\sim+0.60$, and $Y\sim0.250$ on the solar abundance scale of Asplund, Grevesse & Sauval. However, this depends on the accuracy of the model $T_{\rm eff}$ scale which is 50-75 K cooler than our best estimate but within measurement uncertainties. Our best estimate of the age of $47\,$Tuc is 11.8 Gyr, with firm ($3 \sigma$) lower and upper limits of 10.4 and 13.4 Gyr, respectively, in satisfactory agreement with the age derived from the white dwarf cooling sequence if our determination of the distance modulus is adopted.Comment: 19 pages, 8 figures, accepted for publication in MNRA

Living with chronic obstructive pulmonary disease and being followed uip through telemedicine - a phenomenological approach

Chronic obstructive pulmonary disease (COPD) provides substantially reduced health related quality of life (HQoL). Telemonitoring on COPD patients appears to have a positive effect on improving HQoL. This study has a phenomenological approach, and ten informants, who were followed-up between 1 and 3 months in their own homes through telemonitoring of COPD symptoms, narrated their lived experiences of HQoL. The results show that the informants experienced safety and increased knowledge through the digital dialog (telemedicine) with expertise nurses, which indirectly improved their HQoL, and in term lead to increased mastery and control in managing their disease. Several studies show an increased HQoL, but the benefits are still limited and there is a need for further research

Unlocking the limitations: living with chronic obstructive pulmonary disease and receiving care through telemedicine - a phenomenological study

Aims and objectives To describe the lived experiences of quality of life among a group of patients living with chronic obstructive pulmonary disease who were included in a telemedical intervention after hospitalisation for disease exacerbation. Background Patients with chronic obstructive pulmonary disease have high symptom burden, poor control of symptoms and a need for greater requirements in care. Telemedicine can provide benefits for patients with chronic obstructive pulmonary disease by improving self-management. Design Descriptive phenomenological approach. Methods Ten in-depth interviews were conducted with chronic obstructive pulmonary disease patients participating in a telemedical intervention. The collected data were analysed using a descriptive phenomenological research method. Results Living with chronic obstructive pulmonary disease was experienced as creating physical and mental limitations of the diseased body and an increasing identity as a patient, which led to impaired quality of life. Being included in the telemedicine intervention increased accessibility to healthcare services and support from telemedicine nurses. Self-measurement of health data increased participants’ clinical insight and created a mutual clinical language in dialogue with telemedicine nurses, which led to increased quality of life. However, receiving care through telemedicine was also experienced as a dual chore. Conclusions Telemedicine can reduce the perceived limitations imposed by chronic obstructive pulmonary disease through four key elements: (i) improving accessibility to healthcare services, (ii) increasing support from health professionals, (iii) strengthening clinical insight and (iv) developing a mutual clinical language, thus increasing quality of life. The transparency facilitated through telemedicine in this healthcare context encourages open decision-making, where the participants can increase their knowledge and improve acknowledgement of and collaboration with telemedicine nurses. Relevance to clinical practice Telemedicine can be beneficial when rethinking care for chronic obstructive pulmonary disease by providing knowledge on how living with chronic obstructive pulmonary disease can affect the experience of receiving care through telemedicine and further determine for whom telemedicine is useful.måsjekke

Conserving GW scheme for nonequilibrium quantum transport in molecular contacts

We give a detailed presentation of our recent scheme to include correlation effects in molecular transport calculations using the GW approximation within the non-equilibrium Keldysh formalism. We restrict the GW self-energy to the central region, and describe the leads by density functional theory (DFT). A minimal basis of maximally localized Wannier functions is applied both in the central GW region and the leads. The importance of using a conserving, i.e. fully self-consistent, GW self-energy is demonstrated both analytically and by numerical examples. We introduce an effective spin-dependent interaction which automatically reduces self-interaction errors to all orders in the interaction. The scheme is applied to the Anderson model in- and out of equilibrium. In equilibrium at zero temperature we find that GW describes the Kondo resonance fairly well for intermediate interaction strengths. Out of equilibrium we demonstrate that the one-shot G0W0 approximation can produce severe errors, in particular at high bias. Finally, we consider a benzene molecule between featureless leads. It is found that the molecule's HOMO-LUMO gap as calculated in GW is significantly reduced as the coupling to the leads is increased, reflecting the more efficient screening in the strongly coupled junction. For the IV characteristics of the junction we find that HF and G0W0[G_HF] yield results closer to GW than does DFT and G0W0[G_DFT]. This is explained in terms of self-interaction effects and life-time reduction due to electron-electron interactions.Comment: 23 pages, 16 figure

Hybrid Local-Order Mechanism for Inversion Symmetry Breaking

Using classical Monte Carlo simulations, we study a simple statistical mechanical model of relevance to the emergence of polarisation from local displacements on the square and cubic lattices. Our model contains two key ingredients: a Kitaev-like orientation-dependent interaction between nearest neighbours, and a steric term that acts between next-nearest neighbours. Taken by themselves, each of these two ingredients is incapable of driving long-range symmetry breaking, despite the presence of a broad feature in the corresponding heat capacity functions. Instead each component results in a "hidden" transition on cooling to a manifold of degenerate states, the two manifolds are different in the sense that they reflect distinct types of local order. Remarkably, their intersection---\emph{i.e.} the ground state when both interaction terms are included in the Hamiltonian---supports a spontaneous polarisation. In this way, our study demonstrates how local ordering mechanisms might be combined to break global inversion symmetry in a manner conceptually similar to that operating in the "hybrid" improper ferroelectrics. We discuss the relevance of our analysis to the emergence of spontaneous polarisation in well-studied ferroelectrics such as BaTiO$_3$ and KNbO$_3$.Comment: 8 pages, 8 figure

Partly Occupied Wannier Functions

We introduce a scheme for constructing partly occupied, maximally localized Wannier functions (WFs) for both molecular and periodic systems. Compared to the traditional occupied WFs the partly occupied WFs posses improved symmetry and localization properties achieved through a bonding-antibonding closing procedure. We demonstrate the equivalence between bonding-antibonding closure and the minimization of the average spread of the WFs in the case of a benzene molecule and a linear chain of Pt atoms. The general applicability of the method is demonstrated through the calculation of WFs for a metallic system with an impurity: a Pt wire with a hydrogen molecular bridge.Comment: 5 pages, 4 figure