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Molecular photo cross sections with the LCGTO–Xα method using Stieltjes imaging (1990)

Görling, A. ; Rösch, N.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 93 (1990), S. 5563-5572

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: A method for calculating and symmetry analyzing total molecular photoionization cross sections is presented. The technique is based on the LCGTO–Xα method and employs Stieltjes imaging. It allows applications to molecular systems comparable in size to those treated so far with the continuum multiple-scattering Xα method, but avoids the pitfalls of the muffin-tin approximation to the electronic potential. Photo cross sections for valence ionization of CO are found in good agreement with experiment and with previous calculations. From a final state symmetry analysis for the 1π level, the absence of kσ* shape resonance which appears in the 4σ and the 5σ ionization channels is attributed to small transition moments. This is in contrast to a previous treatment where this difference has been rationalized as caused by a channel dependent final state potential. The photoionization cross sections for the four highest valence orbitals of benzene were calculated in better agreement with experiment than found in a previous Xα–SW treatment. The improvement is especially significant for the 1e1g(π) highest occupied molecular orbital where at least part of the experimentally observed structures are attributed to shape resonances. Some of the observed resonance features in the valence orbital photo cross sections of benzene were identified with resonances found in carbon K-shell ionization.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.459626

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Digitale Medien

Molecular photoionization cross sections by the Lobatto technique. I. Valence photoionization (1994)

Wilhelmy, Immanuel ; Ackermann, Lutz ; Görling, Andreas ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 100 (1994), S. 2808-2820

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Details

ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: A method for the calculation of electronic continuum wave functions is presented which is based on the logarithmic derivative version of the Kohn (LDK) variational principle. The variational principle is cast into algebraic form by introducing a finite basis set that consists of spherical harmonic Gaussian-type functions (GTOs) and of Lobatto shape functions with the latter representing the translational part of the basis. A local effective potential which is obtained from density functional theory results in fairly accurate photoionization cross sections. Also studied are asymptotic corrections to the effective potential for the photoelectron which, in many cases, lead to improved results. The Lobatto procedure is applied to the diatomics N2 and CO and to benzene which may be regarded as a prototype for larger non spherical symmetric systems for which the method is targeted. For the two diatomics, results in excellent agreement with experiment have been found. For benzene the results are compared to those obtained by the Stieltjes–Tchebychev (ST) imaging technique and by the continuum multiple scattering (CMS) method which both have been applied to similar effective local potentials. Comparison with the ST imaging technique shows that the LDK Lobatto (LDKL) method provides qualitatively similar results, but the LDKL cross sections are of higher resolution and allow a more detailed analysis because of the explicit determination of the continuum wave function. For most of the valence orbitals of benzene the CMS method does not lead to satisfactory agreement with experiment due to the well-known deficiencies of this technique. The LDKL method implemented with a combined basis set does not suffer from the limitations of the ST and the CMS methods, but remains applicable to larger-size molecules.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.466475

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