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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Distance Dependence of Electronic Coupling through Trans Alkyl Chains: Effects of Electron Correlation
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Distance Dependence of Electronic Coupling through Trans Alkyl Chains: Effects of Electron Correlation

机译：跨烷基链电子耦合的距离依赖性：电子相关性的影响

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摘要

Electronic coupling between CH_2 π donor/acceptor groups at the termini of trans alkyl chains [H_2C-(CH_2)_(n - 2)-CH_2, n = 4-16] was investigated using Hartree-Fock (HF) theory, second-order Moller-Plesset perturbation theory (MP2), and density functional theory (DFT). For each method the couplings in the ions were calculated in two ways: (1) the difference in donor/acceptor orbital energies [Koopmans' theorem (KT)] and (2) the difference between the ground state and first excited state energy of the ions (ΔE). The distance dependence of the coupling in anions was found to be independent of the method used, indicating that electron correlation has little effect. In contrast, the distance dependence of the couplings in cations was very dependent on the method used. For cations, couplings from ΔDFT calculations have a weak distance dependence (β < 0.4) similar to that found previously for KT couplings from HF (β ～ 0.4), while couplings from KT(DFT) and ΔMP2 calculations have a stronger distance dependence (β～ 0.6-0.7) similar to that found previously from ΔHF calculations. When energetics are examined, it appears that the weak distance dependence for some of the methods may arise from small energy differences between the donor/acceptor levels and the energies of the filled orbitals. This was confirmed by calculations on a series of trans alkyls with different donor/acceptor groups (NH_2, SiH_2, PH_2). The couplings for the anions have a stronger distance dependence (β ～ 0.6-0.7) in all of the methods. Finally, it is found that the inclusion of diffuse functions in the basis set does not introduce problems for the calculation of anion couplings by density functional theory, in contrast to ab initio molecular orbital calculations where erratic results are obtained.
机译：使用Hartree-Fock（HF）理论研究了在反烷基链[H_2C-（CH_2）_（n-2）-CH_2，n = 4-16]末端处CH_2π供体/受体基团之间的电子耦合。阶Moller-Plesset微扰理论（MP2）和密度泛函理论（DFT）。对于每种方法，以两种方式计算离子中的耦合：（1）供体/受体轨道能量之差[Koopmans定理（KT）]和（2）离子的基态与第一激发态能之差离子（ΔE）。发现阴离子中偶联的距离依赖性与所用方法无关，表明电子相关性影响很小。相反，阳离子中偶联的距离依赖性非常依赖于所使用的方法。对于阳离子，通过ΔDFT计算得出的耦合具有较弱的距离依赖性（β<0.4），类似于先前从HF中通过KT耦合发现的（β〜0.4），而通过KT（DFT）和ΔMP2计算得到的耦合具有更强的距离依赖性（β （〜0.6-0.7）类似于以前从ΔHF计算得出的结果。当检查高能时，似乎某些方法的弱距离依赖性可能是由于施主/受主能级与填充轨道的能量之间的微小能量差异引起的。通过对具有不同供体/受体基团（NH_2，SiH_2，PH_2）的一系列反式烷基的计算得到证实。在所有方法中，阴离子的偶联具有更强的距离依赖性（β〜0.6-0.7）。最后，发现在基集中包含弥散函数不会对密度耦合理论进行阴离子偶合计算产生任何问题，这与从头算分子轨道计算得出的不稳定结果相反。

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