Félix Martín, Voityuk Alexander A
Institut de Quimica Computational, Departament de Quimica, Universitat de Girona, 17071 Girona, Spain.
J Phys Chem A. 2008 Sep 25;112(38):9043-9. doi: 10.1021/jp803636x. Epub 2008 Aug 28.
We show that the energetics and electronic couplings for excess electron transfer (EET) can be accurately estimated by using unoccupied Kohn-Sham orbitals (UKSO) calculated for neutral pi stacks. To assess the performance of different DFT functionals, we use MS-PT2 results for seven pi stacks of nucleobases as reference data. The DFT calculations are carried out by using the local spin density approximation SVWN, two generalized gradient approximation functionals BP86 and BLYP, and two hybrid functionals B3LYP and BH&HLYP. Best estimations within the UKSO approach are obtained by the B3LYP and SVWN methods. TD DFT calculations provide less accurate values of the EET parameters as compared with the UKSO data. Also, the excess charge distribution in the radical anions is well described by the LUMOs of neutral systems. In contrast, spin-unrestricted DFT calculations of radical anions considerably overestimate delocalization of the excess electron. The excellent results obtained for the ground and excited states of the radical anions (excitation energy, transition dipole moment, electronic coupling, and excess electron distribution) by using UKSO of neutral dimers suggest an efficient strategy to calculate the EET parameters for DNA pi stacks.
我们表明，通过使用为中性π堆积计算的未占据的Kohn-Sham轨道（UKSO），可以准确估计多余电子转移（EET）的能量学和电子耦合。为了评估不同密度泛函理论（DFT）泛函的性能，我们将七个核碱基π堆积的多体微扰理论二级微扰（MS-PT2）结果用作参考数据。DFT计算使用局域自旋密度近似SVWN、两种广义梯度近似泛函BP86和BLYP，以及两种杂化泛函B3LYP和BH&HLYP进行。在UKSO方法中，通过B3LYP和SVWN方法获得了最佳估计值。与UKSO数据相比，含时密度泛函理论（TD DFT）计算提供的EET参数值准确性较低。此外，自由基阴离子中的多余电荷分布可以通过中性体系的最低未占分子轨道（LUMO）很好地描述。相比之下，自由基阴离子的自旋非限制DFT计算大大高估了多余电子的离域。通过使用中性二聚体的UKSO，在自由基阴离子的基态和激发态（激发能、跃迁偶极矩、电子耦合和多余电子分布）方面获得的优异结果表明了一种计算DNA π堆积的EET参数的有效策略。
