Gauge-Origin-Independent Coupled Cluster Singles and Doubles Calculation of Magnetic Circular Dichroism of Azabenzenes and Phosphabenzene Using London Orbitals

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• 作者：Thomas Kj&aelig ; rgaard ; Branislav Jansí ; k ; Poul Jrgensen ; Sonia Coriani ; Josef Michl
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：November 8, 2007
• 年：2007
• 卷：111
• 期：44
• 页码：11278 - 11286
• 全文大小：164K
• 年卷期：v.111,no.44(November 8, 2007)
• ISSN：1520-5215

文摘

A computational study of the Faraday B term of magnetic circular dichroism at the coupled cluster singlesand doubles level is presented for pyridine, pyrazine, pyrimidine, and phosphabenzene. Gauge-originindependence is obtained by expressing the B term as a total derivative of the one-photon dipole transitionstrength and using London orbitals. The high quality of the coupled cluster singles and doubles (CCSD) Bterms makes these useful for the assignment of experimental spectra. Previous assignments of the experimentalspectra based on the qualitative perimeter model are confirmed by the CCSD results for the three azines,while a reassignment is proposed for phosphabenzene. For non-overlapping bands, the B terms calculated atthe equilibrium geometries are in good agreement with the experimental values. For overlapping bands, largedeviations occur. Attributing a line width to the calculated equilibrium B terms leads to a large cancellationof positive and negative contributions. This cancellation may result in a large displacement of the band centermaximum, leading to a large uncertainty in the assignments of "vertical experimental excitation energies"(pyridine). Bands may also completely vanish due to such cancellation (phosphabenzene). Explicit considerationof the cancellation yields simulated theoretical spectra that are in good agreement with experiment once thetheoretical spectra are parallel displaced. A major contribution for this parallel displacement is the shift in theexcitation energies due to correlation beyond CCSD, as seen when comparing vertical CCSD and CC3equilibrium-geometry excitation energies.