Carbon X-ray absorption spectra of fluoroethenes and acetone: A study at the coupled cluster, density functional, and static-exchange levels of theory
Carbon X-ray absorption spectra of fluoroethenes and acetone: A study at the coupled cluster, density functional, and static-exchange levels of theory
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DOI：
10.1063/1.4795835
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发表时间：
2013-03-28
影响因子：
4.4
通讯作者：
Norman, Patrick
中科院分区：
文献类型：
--
作者：
Fransson, Thomas;Coriani, Sonia;Norman, Patrick
使用耦合簇和密度泛函理论（DFT）偏振传播器方法以及静态交换（STEX）方法研究了一系列氟取代乙烯和丙酮的近碳K边X射线吸收精细结构光谱。通过在耦合簇理论中实现复杂的偏振传播器（CPP），可以根据电子相关性来考虑核心电子激发后的弛豫效应，从而使这些效应相对于簇算子中的电子激发能够系统地收敛。耦合聚类结果已被用作评估 DFT 中传播器方法以及特定于状态的静态交换方法的基准。对乙烯和 1,1-二氟乙烯的计算说明了使用非相对论耦合团簇单团簇和团簇双团簇 (CCSD) 的可能性，以及电子相关性和相对论作为能量学标量位移而添加的附加效应。事实证明，使用耦合簇单簇和近似双簇 (CC2)、CCSD 和 DFT（具有库仑衰减交换相关函数）获得的 CPP 光谱可以对氟乙烯、1,1-二氟乙烯、三氟乙烯的化学位移产生出色的预测，并且在 CCSD 和 DFT 的情况下对丙酮具有良好的光谱特征。此后，CPP-DFT 被认为是计算较大 π 共轭系统的 X 射线吸收光谱的可行选择，而 CC2 被认为适用于化学位移，但不适用于精细结构特征的研究。 CCSD 方法以及更近似的 CC2 方法显示出产生与 pi* 共振相关的光谱特征，与实验非常一致，不仅对于上述分子，而且对于乙烯、顺式 1,2-二氟乙烯和四氟乙烯。由于频谱压缩，STEX 方法会低估 pi* 峰分离，这是该方法固有的特征。 (C) 2013 年美国物理研究所。 [http://dx.doi.org/10.1063/1.4795835]
Near carbon K-edge X-ray absorption fine structure spectra of a series of fluorine-substituted ethenes and acetone have been studied using coupled cluster and density functional theory (DFT) polarization propagator methods, as well as the static-exchange (STEX) approach. With the complex polarization propagator (CPP) implemented in coupled cluster theory, relaxation effects following the excitation of core electrons are accounted for in terms of electron correlation, enabling a systematic convergence of these effects with respect to electron excitations in the cluster operator. Coupled cluster results have been used as benchmarks for the assessment of propagator methods in DFT as well as the state-specific static-exchange approach. Calculations on ethene and 1,1-difluoroethene illustrate the possibility of using nonrelativistic coupled cluster singles and doubles (CCSD) with additional effects of electron correlation and relativity added as scalar shifts in energetics. It has been demonstrated that CPP spectra obtained with coupled cluster singles and approximate doubles (CC2), CCSD, and DFT (with a Coulomb attenuated exchange-correlation functional) yield excellent predictions of chemical shifts for vinylfluoride, 1,1-difluoroethene, trifluoroethene, as well as good spectral features for acetone in the case of CCSD and DFT. Following this, CPP-DFT is considered to be a viable option for the calculation of X-ray absorption spectra of larger pi-conjugated systems, and CC2 is deemed applicable for chemical shifts but not for studies of fine structure features. The CCSD method as well as the more approximate CC2 method are shown to yield spectral features relating to pi*-resonances in good agreement with experiment, not only for the aforementioned molecules but also for ethene, cis-1,2-difluoroethene, and tetrafluoroethene. The STEX approach is shown to underestimate pi*-peak separations due to spectral compressions, a characteristic which is inherent to this method. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795835]