Golubeva Anna A, Krylov Anna I
Department of Chemistry, University of Southern California, Los Angeles, CA 90089-0482, USA.
Phys Chem Chem Phys. 2009 Mar 7;11(9):1303-11. doi: 10.1039/b817284f. Epub 2009 Feb 2.
The electronic structure of the ionized pi-stacked and H-bonded uracil dimers as well as that of the monomer, is characterized by the equation-of-motion coupled-cluster method for ionization potentials (EOM-IP). Vertical ionization energies (IEs) for the 5 lowest states of the monomer and the 10 lowest states of the dimers are presented. Non-covalent interactions in the dimers reduce the lowest vertical IE by 0.34 and 0.13 eV in the pi-stacked and H-bonded dimers, respectively. The electronic spectra of the cations are also presented. The two dimer cations feature intense charge resonance bands at 0.52 and 0.11 eV, respectively. The position and intensity of the bands are sensitive to the dimer structures, for example, the geometric relaxation in the pi-stacked dimer blue-shifts the CR band by more than 1 eV and results in a threefold intensity increase. The results of the calculations are rationalized within the dimer molecular orbital - linear combination of fragment molecular orbitals (DMO-LCFMO) framework. The basis set effects and energy additivity schemes are also discussed.
采用运动方程耦合簇方法计算电离势（EOM - IP），对电离的π堆积和氢键连接的尿嘧啶二聚体以及单体的电子结构进行了表征。给出了单体最低5个态和二聚体最低10个态的垂直电离能（IE）。二聚体中的非共价相互作用使π堆积二聚体和氢键连接二聚体的最低垂直电离能分别降低了0.34 eV和0.13 eV。还给出了阳离子的电子光谱。两种二聚体阳离子分别在0.52 eV和0.11 eV处有强烈的电荷共振带。这些谱带的位置和强度对二聚体结构敏感，例如，π堆积二聚体中的几何弛豫使电荷共振带蓝移超过1 eV，并导致强度增加三倍。在二聚体分子轨道 - 片段分子轨道线性组合（DMO - LCFMO）框架内对计算结果进行了合理解释。还讨论了基组效应和能量加和方案。
