Effect of dispersion correction on the Au(1 1 1)-H2O interface: A first-principles study

A theoretical study of the H2O-Au(1 1 1) interface based on first principles density functional theory (DFT) calculations with and without inclusion of dispersion correction is reported. Three different computational approaches are considered. First, the standard generalized gradient approximation (GGA) functional PBE is employed. Second, an additional energy term is further included that adds a semi-empirically derived dispersion correction (PBE-D2), and, finally, a recently proposed functional that includes van der Waals (vdW) interactions directly in its functional form (optB86b-vdW) was used to represent the state-of-the art of DFT functionals. The monomeric water adsorption was first considered in order to explore the dependency of geometry on the details of the model slab used to represent it (size, thickness, coverage). When the dispersion corrections are included the Au-H2O interaction is stronger, as manifested by the smaller dAu-O and stronger adsorption energies. Additionally, the interfacial region between Au(1 1 1) slab surfaces and a liquid water layer was investigated with Born-Oppenheimer molecular dynamics (BOMD) using the same functionals. Two or three interfacial orientations can be determined, depending on the theoretical methodology applied. Closest to the surface, H2O is adsorbed O-down, whereas further away it is oriented with one OH bond pointing to the surface and the molecular plane parallel to the normal direction. For the optB86b-vdW functional a third orientation is found where one H atom points into the bulk water layer and the second OH bond is oriented parallel to the metal surface. As for the water density in the first adsorption layer we find a very small increase of roughly 8%. From the analysis of vibrational spectra a weakening of the H-bond network is observed upon the inclusion of the Au(1 1 1) slab, however, no disruption of H-bonds is observed. While the PBE and PBE-D2 spectra are very similar, the optB86b-vdW spectrum shows that the H-bonds are even more weakened.Ministerio de Ciencia e Innovación de España-MAT2012-31526 y CSD2008-002

Electronic and structural properties of metal chalcogenides quantum dots. A theoretical study based on first-principles calculations

Tesis descargada desde TESEO.En esta tesis se presenta resultados de puntos cuánticos (PCs) que se ha descrito a través de métodos ab-initio. Se consideran las propiedades geométricas, electrónicas, y ópticas para obtener una descripción general de los PCs. Se ha usado CdSe y FeS2 como PCs. Se ha estudiado el efecto de ligandos alifáticos y aromáticos en la estructura electrónica y en el espectro de absorción. En un siguiente paso, se ha sensibilizado nanoestructuras de TiO2 con PCs consistiendo de CdSe, así simulando una celda solar sensibilizada con puntos cuánticos (CSSPC). Por un lado, se ha sensibilizado nanoclusters de TiO2. Por otro lado, se ha modelado nanotubos de TiO2 que así representan un modelo realista de una CSSPC

Hermeneutics and Nature

This paper contributes to the on-going research into the ways in which the humanities transformed the natural sciences in the late Eighteenth and early Nineteenth Centuries. By investigating the relationship between hermeneutics -- as developed by Herder -- and natural history, it shows how the methods used for the study of literary and artistic works played a crucial role in the emergence of key natural-scientific fields, including geography and ecology

Long-term risk of adverse outcomes according to atrial fibrillation type

Sustained forms of atrial fibrillation (AF) may be associated with a higher risk of adverse outcomes, but few if any long-term studies took into account changes of AF type and co-morbidities over time. We prospectively followed 3843 AF patients and collected information on AF type and co-morbidities during yearly follow-ups. The primary outcome was a composite of stroke or systemic embolism (SE). Secondary outcomes included myocardial infarction, hospitalization for congestive heart failure (CHF), bleeding and all-cause mortality. Multivariable adjusted Cox proportional hazards models with time-varying covariates were used to compare hazard ratios (HR) according to AF type. At baseline 1895 (49%), 1046 (27%) and 902 (24%) patients had paroxysmal, persistent and permanent AF and 3234 (84%) were anticoagulated. After a median (IQR) follow-up of 3.0 (1.9; 4.2) years, the incidence of stroke/SE was 1.0 per 100 patient-years. The incidence of myocardial infarction, CHF, bleeding and all-cause mortality was 0.7, 3.0, 2.9 and 2.7 per 100 patient-years, respectively. The multivariable adjusted (a) HRs (95% confidence interval) for stroke/SE were 1.13 (0.69; 1.85) and 1.27 (0.83; 1.95) for time-updated persistent and permanent AF, respectively. The corresponding aHRs were 1.23 (0.89, 1.69) and 1.45 (1.12; 1.87) for all-cause mortality, 1.34 (1.00; 1.80) and 1.30 (1.01; 1.67) for CHF, 0.91 (0.48; 1.72) and 0.95 (0.56; 1.59) for myocardial infarction, and 0.89 (0.70; 1.14) and 1.00 (0.81; 1.24) for bleeding. In this large prospective cohort of AF patients, time-updated AF type was not associated with incident stroke/SE

Ionic Interactions in Biological and Physical Systems: a Variational Treatment

Chemistry is about chemical reactions. Chemistry is about electrons changing their configurations as atoms and molecules react. Chemistry studies reactions as if they occurred in ideal infinitely dilute solutions. But most reactions occur in nonideal solutions. Then everything (charged) interacts with everything else (charged) through the electric field, which is short and long range extending to boundaries of the system. Mathematics has recently been developed to deal with interacting systems of this sort. The variational theory of complex fluids has spawned the theory of liquid crystals. In my view, ionic solutions should be viewed as complex fluids. In both biology and electrochemistry ionic solutions are mixtures highly concentrated (~10M) where they are most important, near electrodes, nucleic acids, enzymes, and ion channels. Calcium is always involved in biological solutions because its concentration in a particular location is the signal that controls many biological functions. Such interacting systems are not simple fluids, and it is no wonder that analysis of interactions, such as the Hofmeister series, rooted in that tradition, has not succeeded as one would hope. We present a variational treatment of hard spheres in a frictional dielectric. The theory automatically extends to spatially nonuniform boundary conditions and the nonequilibrium systems and flows they produce. The theory is unavoidably self-consistent since differential equations are derived (not assumed) from models of (Helmholtz free) energy and dissipation of the electrolyte. The origin of the Hofmeister series is (in my view) an inverse problem that becomes well posed when enough data from disjoint experimental traditions are interpreted with a self-consistent theory.Comment: As prepared for Faraday Discussion, Pavel Jungwirth Organizer, 3 - 5 September 2012, Queens College Oxford, UK on Ion Specific Hofmeister Effects. Version 2 has significant typo corrections in eq. 1 and eq. 4, and has been reformatted to be easier to rea

Development and Validation of a Risk Score for Chronic Kidney Disease in HIV Infection Using Prospective Cohort Data from the D:A:D Study

Ristola M. on työryhmien DAD Study Grp ; Royal Free Hosp Clin Cohort ; INSIGHT Study Grp ; SMART Study Grp ; ESPRIT Study Grp jäsen.Background Chronic kidney disease (CKD) is a major health issue for HIV-positive individuals, associated with increased morbidity and mortality. Development and implementation of a risk score model for CKD would allow comparison of the risks and benefits of adding potentially nephrotoxic antiretrovirals to a treatment regimen and would identify those at greatest risk of CKD. The aims of this study were to develop a simple, externally validated, and widely applicable long-term risk score model for CKD in HIV-positive individuals that can guide decision making in clinical practice. Methods and Findings A total of 17,954 HIV-positive individuals from the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D) study with >= 3 estimated glomerular filtration rate (eGFR) values after 1 January 2004 were included. Baseline was defined as the first eGFR > 60 ml/min/1.73 m2 after 1 January 2004; individuals with exposure to tenofovir, atazanavir, atazanavir/ritonavir, lopinavir/ritonavir, other boosted protease inhibitors before baseline were excluded. CKD was defined as confirmed (>3 mo apart) eGFR In the D:A:D study, 641 individuals developed CKD during 103,185 person-years of follow-up (PYFU; incidence 6.2/1,000 PYFU, 95% CI 5.7-6.7; median follow-up 6.1 y, range 0.3-9.1 y). Older age, intravenous drug use, hepatitis C coinfection, lower baseline eGFR, female gender, lower CD4 count nadir, hypertension, diabetes, and cardiovascular disease (CVD) predicted CKD. The adjusted incidence rate ratios of these nine categorical variables were scaled and summed to create the risk score. The median risk score at baseline was -2 (interquartile range -4 to 2). There was a 1: 393 chance of developing CKD in the next 5 y in the low risk group (risk score = 5, 505 events), respectively. Number needed to harm (NNTH) at 5 y when starting unboosted atazanavir or lopinavir/ritonavir among those with a low risk score was 1,702 (95% CI 1,166-3,367); NNTH was 202 (95% CI 159-278) and 21 (95% CI 19-23), respectively, for those with a medium and high risk score. NNTH was 739 (95% CI 506-1462), 88 (95% CI 69-121), and 9 (95% CI 8-10) for those with a low, medium, and high risk score, respectively, starting tenofovir, atazanavir/ritonavir, or another boosted protease inhibitor. The Royal Free Hospital Clinic Cohort included 2,548 individuals, of whom 94 individuals developed CKD (3.7%) during 18,376 PYFU (median follow-up 7.4 y, range 0.3-12.7 y). Of 2,013 individuals included from the SMART/ESPRIT control arms, 32 individuals developed CKD (1.6%) during 8,452 PYFU (median follow-up 4.1 y, range 0.6-8.1 y). External validation showed that the risk score predicted well in these cohorts. Limitations of this study included limited data on race and no information on proteinuria. Conclusions Both traditional and HIV-related risk factors were predictive of CKD. These factors were used to develop a risk score for CKD in HIV infection, externally validated, that has direct clinical relevance for patients and clinicians to weigh the benefits of certain antiretrovirals against the risk of CKD and to identify those at greatest risk of CKD.Peer reviewe

Effect of Capping Ligands and TiO₂ Supporting on the Optical Properties of a (CdSe)₁₃ Cluster

The influence of different aliphatic and aromatic ligand molecules on the electronic properties of CdSe quantum dots (QDs) has been examined by employing density functional theory (DFT). Optical spectra were simulated with the real-time time-dependent DFT (RT-TDDFT) methodology. The assignment of the first absorption peak features that occur in these spectra was done by taking into account the composition of the frontier molecular orbitals (MOs) of the different systems. While the aliphatic ligands consideredamine, thiol, and phospine oxidesdid not show any major influence on the electronic absorption spectra, some of the aromatic ligands do have a noticeable impact on the optoelectronic properties of the QD. Aromatic ligands are mainly aniline-type molecules; additionally, a thiophenol and uracil were employed to saturate the dangling bonds on the Cd atoms. Finally, a more realistic model of a QD-sensitized solar cell consisting of methylamine-capped (CdSe)₁₃ cluster linked to a TiO₂ nanoparticle through a mercaptopropionate bridge was considered. The simulations again show that the lowest electronic excitation takes place within the QD subunit, demonstrating the indirect nature of the electron injection mechanism operating in these solar cells

Effect of Capping Ligands and TiO₂ Supporting on the Optical Properties of a (CdSe)₁₃ Cluster

The influence of different aliphatic and aromatic ligand molecules on the electronic properties of CdSe quantum dots (QDs) has been examined by employing density functional theory (DFT). Optical spectra were simulated with the real-time time-dependent DFT (RT-TDDFT) methodology. The assignment of the first absorption peak features that occur in these spectra was done by taking into account the composition of the frontier molecular orbitals (MOs) of the different systems. While the aliphatic ligands consideredamine, thiol, and phospine oxidesdid not show any major influence on the electronic absorption spectra, some of the aromatic ligands do have a noticeable impact on the optoelectronic properties of the QD. Aromatic ligands are mainly aniline-type molecules; additionally, a thiophenol and uracil were employed to saturate the dangling bonds on the Cd atoms. Finally, a more realistic model of a QD-sensitized solar cell consisting of methylamine-capped (CdSe)₁₃ cluster linked to a TiO₂ nanoparticle through a mercaptopropionate bridge was considered. The simulations again show that the lowest electronic excitation takes place within the QD subunit, demonstrating the indirect nature of the electron injection mechanism operating in these solar cells