Atoms in boxes: from confined atoms to electron-atom scattering

We show that both confined atoms and electron-atom scattering can be described by a unified basis set method. The central idea behind this method is to place the atom inside a hard potential sphere, enforced by a standard Slater type basis set multiplied by a cutoff factor. For confined atoms, where the wall is placed close to the atomic nucleus, we show how the energy of the highest occupied atomic orbital and the static polarizability of helium and neon atoms evolve with the confinement radius. To our knowledge, these are the first confined atom polarizability calculations that include correlation, through the use of time-dependent density-functional theory. By placing the atom in a large spherical box, with a wall outside the electron density, we obtain scattering phase shifts using a recently developed method [M. van Faassen, A. Wasserman, E. Engel, F. Zhang, and K. Burke, Phys. Rev. Lett. {\bf 99}, 043005 (2007)]. We show that the basis set method gives identical results to previously obtained phase shifts for $e$-H and $e$-He${}^{+}$ scattering.Comment: 8 pages, 6 figures, submitted to Journal of Chemical Physic

Time-dependent density functional theory of high excitations: To infinity, and beyond

We review the theoretical background for obtaining both quantum defects and scattering phase shifts from time-dependent density functional theory. The quantum defect on the negative energy side of the spectrum and the phase shift on the positive energy side merge continuously at E=0, allowing both to be found by the same method. We illustrate with simple one-dimensional examples: the spherical well and the delta well potential. As an example of a real system, we study in detail elastic electron scattering from the He${}^{+}$ ion. We show how the results are influenced by different approximations to the unknown components in (time-dependent) density functional theory: the ground state exchange-correlation potential and time-dependent kernel. We also revisit our previously obtained results for $e$-H scattering. Our results are remarkably accurate in may cases, but fail qualitatively in others.Comment: Resubmitted version, Changed acknowledgments, 17 pages including supplementary table, submitted to PCCP themed issue on time-dependent density-functional theor

Development and applications of novel strategies for the enhanced mass spectrometric quantification of biogenic amines

Liquid chromatography in combination with triple-quadrupole mass spectrometry (LC-MS/MS) is rapidly developing as the analytical technique of choice for quantitative analysis of small molecules such as steroid hormones, vitamins, and biogenic amines. In recent years, there has been a shift towards widespread adaption of LC-MS/MS in the field of laboratory medicine. One of the compound classes that remains difficult to analyze especially in plasma, are the biogenic amines. Biogenic amines are biologically active compounds containing one or more amine groups and are produced from amino acids. Dopamine, norepinephrine, and epinephrine are synthesized from tyrosine; serotonin from tryptophan, and histamine from histidine. They are regarded as the “classic” biogenic amines, and foremost known for their roles as neurotransmitter. Biogenic amines are important markers for the diagnosis of neuroendocrine neoplasia.Neuroendocrine tumors are rare tumors that originate from cells of the endocrine and nervous system. One common characteristic of neuroendocrine tumors is that they have the ability to take up and metabolize amine precursors. Excessive production of biogenic amines may result in endocrine related complaints. No methods were available that enable the simultaneous profiling of all potentially relevant biogenic amine markers in one profile. We developed new approaches allowing simultaneous detection of these amines, their precursors, and metabolites that are of great interest. They could potentially aid in the diagnosis and management of neuroendocrine tumors.The aim of this thesis was to investigate and develop novel approaches for the enhanced mass spectrometric detection of neuroendocrine biomarkers

Time-Dependent Quasiparticle Current Density Functional Theory of X-Ray Nonlinear Response Functions

A real-space representation of the current response of many-electron systems with possible applications to x-ray nonlinear spectroscopy and magnetic susceptibilities is developed. Closed expressions for the linear, quadratic and third-order response functions are derived by solving the adiabatic Time Dependent Current Density Functional (TDCDFT) equations for the single-electron density matrix in Liouville space.Comment: 11 page