Theory of elastic and inelastic X-ray scattering

X-rays have been widely exploited to unravel the structure of matter since their discovery in 1895. Nowadays, with the emergence of new X-ray sources with higher intensity and very short pulse duration, notably X-ray Free Electron Lasers, the number of experiments that may be considered in the X-ray regime has increased dramatically, making the characterization of gas phase atoms and molecules in space and time possible. This thesis explores in the theoretical analysis and calculation of X-ray scattering atoms and molecules, far beyond the independent atom model. Amethod to calculate inelastic X-ray scattering from atoms and molecules is presented. The method utilizes electronic wavefunctions calculated using ab-initio electronic structure methods. Wavefunctions expressed in Gaussian type orbitals allow for efficient calculations based on analytical Fourier transforms of the electron density and overlap integrals. The method is validated by extensive calculations of inelastic cross-sections in H, He+, He, Ne, C, Na and N2. The calculated cross-sections are compared to cross-sections from inelastic X-ray scattering experiments, electron energy-loss spectroscopy, and theoretical reference values. We then begin to account for the effect of nuclear motion, in the first instance by predicting elastic X-ray scattering from state-selected molecules. We find strong signatures corresponding to the specific vibrational and rotational state of (polyatomic) molecules. The ultimate goal of this thesis is to study atomic and molecular wavepackets using time-resolved X-ray scattering. We present a theoretical framework based on quantum electrodynamics and explore various elastic and inelastic limits of the scattering expressions. We then explore X-ray scattering from electronic wavepackets, following on from work by other groups, and finally examine the time-resolved X-ray scattering from non-adiabatic electronic-nuclear wavepackets in the H2 molecule, demonstrating the importance of accounting for the inelastic effects

Excited Electronic States in Total Isotropic Scattering from Molecules

Ultrafast x-ray scattering experiments are routinely analyzed in terms of the isotropic scattering component. Here we present an analytical method for calculating total isotropic scattering directly from ab initio two-electron densities of ground and excited electronic states. The method is generalized to compute isotropic elastic, inelastic, and coherent mixed scattering. The computational results focus on the potential for differentiating between electronic states and on the composition of the total scattering in terms of elastic and inelastic scattering. By studying the umbrella motion in the first excited state of ammonia, we show that the associated electron density redistribution leaves a comparably constant fingerprint in the total signal that is similar in magnitude to the contribution from the changes in molecular geometry

Elastic X-ray scattering from state-selected molecules

International audienceThe characterization of electronic, vibrational, and rotational states using elastic (coherent) X-ray scattering is considered. The scattering is calculated directly from complete active space self-consistent field level ab initio wavefunctions for H-2 molecules in the ground-state X-1 Sigma(+)(g) and first-excited EF1 Sigma(+)(g) electronic states. The calculated scattering is compared to recent experimental measurements [Y.-W. Liu et al., Phys. Rev. A 89, 014502 (2014)], and the influence of vibrational and rotational states on the observed signal is examined. The scaling of the scattering calculations with basis set is quantified, and it is found that energy convergence of the ab initio calculations is a good indicator of the quality of the scattering calculations. Published by AIP Publishing

Practical update of the Recommendations Published by the Psoriasis Group of the Spanish Academy of Dermatology and Venereology (GPS) on the Treatment of Psoriasis with Biologic Therapy. Part 1. Concepts and General Management of Psoriasis with Biologic Therapy

Justificación y objetivos La aprobación de un gran número de nuevos fármacos en los últimos años y los cambios en el paradigma de tratamiento de la psoriasis hacen recomendable un nuevo documento de recomendaciones del GPS para el tratamiento de la psoriasis moderada-grave. Metodología Para la elaboración del consenso se siguió la metodología de grupos nominales, con ayuda de una scoping review. Tras designar a un coordinador, se seleccionó un grupo de integrantes del GPS. El coordinador definió los objetivos y puntos clave del documento y, con ayuda de un documentalista, se realizó una scoping review incluyendo datos de Medline, Embase y Cochrane Library (hasta enero del 2021). Se seleccionaron revisiones sistemáticas, metaanálisis y ensayos clínicos no incluidos en las mismas, así como estudios de calidad en vida real. Se revisaron otras guías de práctica clínica y documentos de consenso nacionales e internacionales sobre el manejo de la psoriasis moderada-grave. El coordinador generó una serie de recomendaciones preliminares que fueron evaluadas y modificadas en una reunión de grupo nominal. Tras varios procesos de revisión, que incluyeron la revisión externa por parte de los miembros del GPS, se redactó el documento definitivo. Resultados En el documento se incluyen principios generales sobre el tratamiento de los pacientes con psoriasis moderada-grave, la definición de objetivos terapéuticos y los criterios de indicación y selección de tratamiento tanto en primera como en sucesivas líneas terapéuticas de fármacos biológicos. Se abordan asimismo cuestiones prácticas como el fracaso terapéutico o el mantenimiento de la respuesta.Background and objectives A new, updated AEDV Psoriasis Group consensus document on the treatment of moderate to severe psoriasis was needed owing to the approval, in recent years, of a large number of new drugs and changes in the treatment paradigm. Methodology The consensus document was developed using the nominal group technique and a scoping review. First, a designated coordinator selected a group of Psoriasis Group members for the panel. The coordinator defined the objectives and key points for the document and, with the help of a documentalist, conducted a scoping review of articles in Medline, Embase, and the Cochrane Library up to January 2021. The review included systematic reviews and meta-analyses as well as clinical trials not included in those studies and high-quality real-world studies. National and international clinical practice guidelines and consensus documents on the management of moderate to severe psoriasis were also reviewed. Based on these reviews, the coordinator drew up a set of proposed recommendations, which were then discussed and modified in a nominal group meeting. After several review processes, including external review by other GPs members, the final document was drafted. Results The present guidelines include general principles for the treatment of patients with moderate to severe psoriasis and also define treatment goals and criteria for the indication of biologic therapy and the selection of initial and subsequent therapies. Practical issues, such as treatment failure and maintenance of response, are also addressed