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Time dependent density functional theory study of charge-transfer and intramolecular electronic excitations in acetone–water systems


Bernasconi, L; Sprik, M; Hutter, J (2003). Time dependent density functional theory study of charge-transfer and intramolecular electronic excitations in acetone–water systems. Journal of Chemical Physics, 119(23):12417.

Abstract

A recently introduced formulation of time dependent linear response density functional theory within the plane-wave pseudopotential framework [J. Hutter, J. Chem. Phys. 118, 3928 (2003)] is applied to the study of solvent shift and intensity enhancement effects of the (1)A(2) n-->pi{*} electronic transition in acetone, treating solute and solvent at the same level of theory. We propose a suitable formalism for computing transition intensities based on the modern theory of polarization, which is applicable to condensed-phase and finite systems alike. The gain in intensity brought about by thermal fluctuations is studied in molecular acetone at room temperature, and in gas-phase (CH3)(2)CO.(H2O)(2) at 25 K. The latter system is characterized by the appearance of relatively intense features in the low-energy region of the spectrum, attributable to spurious solvent-->solute charge-transfer excitations created by deficiencies in the DFT methodology. The n-->pi{*} transition can be partially isolated from the charge-transfer bands, yielding a blueshift of 0.17 eV with respect to gas-phase acetone. This analysis is then carried over to a solution of acetone in water, where further complications are encountered in the from of a solute-->solvent charge transfer excitations overlapping with the n-->pi{*} band. The optically active occupied states are found to be largely localized on either solute or solvent, and using this feature we were again able to isolate the physical n-->pi{*} band and compute the solvatochromic shift. The result of 0.19 eV is in good agreement with experiment, as is the general increase in the mean oscillator strength of the transition. The unphysical charge transfers are interpreted in terms of degeneracies in the spectrum of orbital energies of the aqueous acetone solution.

A recently introduced formulation of time dependent linear response density functional theory within the plane-wave pseudopotential framework [J. Hutter, J. Chem. Phys. 118, 3928 (2003)] is applied to the study of solvent shift and intensity enhancement effects of the (1)A(2) n-->pi{*} electronic transition in acetone, treating solute and solvent at the same level of theory. We propose a suitable formalism for computing transition intensities based on the modern theory of polarization, which is applicable to condensed-phase and finite systems alike. The gain in intensity brought about by thermal fluctuations is studied in molecular acetone at room temperature, and in gas-phase (CH3)(2)CO.(H2O)(2) at 25 K. The latter system is characterized by the appearance of relatively intense features in the low-energy region of the spectrum, attributable to spurious solvent-->solute charge-transfer excitations created by deficiencies in the DFT methodology. The n-->pi{*} transition can be partially isolated from the charge-transfer bands, yielding a blueshift of 0.17 eV with respect to gas-phase acetone. This analysis is then carried over to a solution of acetone in water, where further complications are encountered in the from of a solute-->solvent charge transfer excitations overlapping with the n-->pi{*} band. The optically active occupied states are found to be largely localized on either solute or solvent, and using this feature we were again able to isolate the physical n-->pi{*} band and compute the solvatochromic shift. The result of 0.19 eV is in good agreement with experiment, as is the general increase in the mean oscillator strength of the transition. The unphysical charge transfers are interpreted in terms of degeneracies in the spectrum of orbital energies of the aqueous acetone solution.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:December 2003
Deposited On:27 Mar 2009 07:30
Last Modified:01 Jun 2016 13:00
Publisher:American Institute of Physics
ISSN:0021-9606
Additional Information:Copyright 2003 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Chemical Physics, 119(23):12417 and may be found at http://dx.doi.org/10.1063/1.1625633
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:10.1063/1.1625633
Permanent URL: http://doi.org/10.5167/uzh-3186

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