Ab Initio Study of the Ionization of the DNA Bases: Ionization Potentials and Excited States of the Cations
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- 作者：Emilie Cauë ; t ; Dominique Dehareng ; Jacques Lié ; vin
- 刊名：Journal of Physical Chemistry A
- 出版年：2006
- 出版时间：July 27, 2006
- 年：2006
- 卷：110
- 期：29
- 页码：9200 - 9211
- 全文大小：345K
- 年卷期：v.110,no.29(July 27, 2006)
- ISSN：1520-5215
文摘
The ionization of the four DNA bases is investigated by means of ab initio calculations. Accurate values ofthe gas-phase vertical and adiabatic ionization potentials (IP) are obtained at the MP2/6-31G(2d(0.8,
d),p)level of theory. The need of introducing extra polarization to the standard 6-31G(d,p) basis set is demonstratedby test calculations and an optimal value of d = 0.1 is obtained. Ionization to electronically excited radicalcations is also considered. The low-lying excited states of the cations are characterized for the first time. Thetopology of the corresponding potential energy surfaces is qualitatively described in terms of the stationarypoints (minima and saddle points) located on these surfaces. A conical intersection is characterized for thefirst time on the ground-state potential energy surface of all cations. It arises from the crossing of the adiabaticsurfaces of the ground and first excited state at planar geometries. A nonplanar minimum is observed for thecytosine cation only. The geometry and electronic changes occurring along these surfaces are analyzed, leadingto a comparison between the different nucleobase cations. The study of larger ionized systems related toDNA is rendered possible thanks to the optimized medium size basis set proposed in this work, as exemplifiedby the calculation of the IP of a stacked dimer of guanines.
d),p)level of theory. The need of introducing extra polarization to the standard 6-31G(d,p) basis set is demonstratedby test calculations and an optimal value of d = 0.1 is obtained. Ionization to electronically excited radicalcations is also considered. The low-lying excited states of the cations are characterized for the first time. Thetopology of the corresponding potential energy surfaces is qualitatively described in terms of the stationarypoints (minima and saddle points) located on these surfaces. A conical intersection is characterized for thefirst time on the ground-state potential energy surface of all cations. It arises from the crossing of the adiabaticsurfaces of the ground and first excited state at planar geometries. A nonplanar minimum is observed for thecytosine cation only. The geometry and electronic changes occurring along these surfaces are analyzed, leadingto a comparison between the different nucleobase cations. The study of larger ionized systems related toDNA is rendered possible thanks to the optimized medium size basis set proposed in this work, as exemplifiedby the calculation of the IP of a stacked dimer of guanines.