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- Carravetta, V., et al.
(författare)
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A screened static-exchange potential for core electron excitations
- 2001
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Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 263:03-feb, s. 231-242
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Tidskriftsartikel (refereegranskat)abstract
- We explore the use of a screened potential for static exchange calculations of core electron excitations, and to which extent this potential can relieve the main limitation of the static exchange method, namely the non-account of the residual screening in the presence of the excited electron. The screened potential is obtained by projecting the target state on a set of polarized orbitals, giving origin to a fully screened potential. Applications are presented and discussed for X-ray absorption spectra of a set of molecules of different size and type. It is found that with the little extra computational effort using the screened potential, the low-energy part of the spectra is generally improved, while the error in the term values are roughly of equal magnitude but of different sign compared to the normal static-exchange calculation. Various aspects of the screened and un-screened static-exchange approximations are analyzed in comparison with other techniques.
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- Gel'mukhanov, Faris, et al.
(författare)
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Anisotropic EXAFS measured in the Raman mode : a way to determine bond angles in randomly oriented species
- 2001
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 34:5, s. 869-879
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that, contrary to the case of ordinary EXAFS measurements, EXAFS measured in the Raman mode is polarization sensitive for randomly oriented systems. This fact can be used to predict bond angles and gives an opportunity for a complete structural determination of gaseous or amorphous systems.
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- Kaznacheyev, K., et al.
(författare)
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Innershell absorption Spectroscopy of amino acids
- 2002
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 106:13, s. 3153-3168
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Tidskriftsartikel (refereegranskat)abstract
- We present comprehensive measurements of the C (carbon) K edge near-edge X-ray absorption (NEXAFS) spectra of all 20 amino acids commonly occurring in nature. Qualitative trends among the spectra of amino acids with similar chemical character are identified and spectral features are compared with extensive ab initio calculations. The contributions of individual units and substitutional groups have been determined to explore their fingerprinting character using the building block concept. Several such units are found. Two that give particularly clear features in the C Is NEXAFS spectra are the carboxyl group (which can be clearly identified by a pronounced structure due to the C 1s-->pi*c-o transition with maximum at 288.65(5) eV) and modified phenol rings in aromatic amino acids (which give sharp C 1s-->pi*c=o structures). The latter transitions are located around 285 cV, and their shape is specific for each aromatic amino acid. Other building blocks, such as the CNHn group and the CH, CC, CO, CN pair bonds, are also identified, although their characteristic features are less pronounced in the C K edge spectra than the carboxylic and aromatic structures. This study provides the basis for rigorous assignment of the NEXAFS spectra of the amino acids, and will be helpful in developing X-ray absorption spectroscopy for quantitative analysis of proteins.
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- Kolczewski, C., et al.
(författare)
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Detailed study of pyridine at the C1s and N1s ionization thresholds : The influence of the vibrational fine structure
- 2001
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 115:14, s. 6426-6437
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Tidskriftsartikel (refereegranskat)abstract
- High resolution, vibrationally resolved, near-edge x-ray absorption fine structure (NEXAFS) spectra at the C 1s and N 1s ionization thresholds of pyridine and deuterated d(5)-pyridine in the gas phase have been recorded. The high resolution of 65 meV (150 meV) at the C s (N 1s) ionization thresholds reveals vibrational structures in the spectra. Detailed ab initio and density functional theory (DFT) calculations were performed to interpret the experimental spectra and to assign the observed peaks. In particular we focused on the previously unexplained intensity ratio for the two components of the C1s -->1 pi* transition. For this transition the vibrational structure is included through a linear coupling model in the DFT calculations and leads to the experimentally observed similar to2:3 intensity ratio between the two pi* components in the C1s spectrum rather than the similar to3:2 ratio obtained without vibrational effects. After inclusion of relaxation effects in the excited states, in addition to the vibrational effects, both theoretical methods yield almost perfect agreement with experiment.
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| 8. |
- Plashkevych, O., et al.
(författare)
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Calculations of valence electron binding energies using Kohn-Sham theory and transition potentials
- 2000
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 106:1, s. 51-63
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the success in computing X-ray photoelectron binding energies and chemical shifts in the core region we apply the Kohn-Sham density functional and transition potential methodology to calculations of binding energies in the valence electron region. Accurate predictions of binding energies over a large energy interval are obtained for a set of molecules for which the quasi-particle approximation holds, but which still have been considered notoriously difficult. The accuracy is found to be a few tenths of an eV in the outermost valence region, slightly poorer in the intermediate region, and seems to be maintained with increasing size of the system.
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| 9. |
- Plashkevych, O, et al.
(författare)
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Calculations of valence electron binding energies using Kohn-Sham theory and transition potentials
- 2000
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Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 106:1, s. 51-63
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the success in computing X-ray photoelectron binding energies and chemical shifts in the core region we apply the Kohn-Sham density functional and transition potential methodology to calculations of binding energies in the valence electron re
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