What a difference a decade has not made: the murky electronic structure of iron monocyanide (FeCN) and iron monoisocyanide (FeNC).
What a difference a decade has not made: the murky electronic structure of iron monocyanide (FeCN) and iron monoisocyanide (FeNC).
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十年来并没有带来多大的变化：一氰化铁 (FeCN) 和一异氰化铁 (FeNC) 的模糊电子结构。
DOI：
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发表时间：
2015
影响因子：
2.9
通讯作者：
Nathan J. DeYonker
中科院分区：
文献类型：
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作者：
Nathan J. DeYonker
已知在中性基团FeCN(FeCN)和FeNc(FeNc)的四重态中存在强大的多参考特征，甚至比有争议的FeH自由基(现在明确地知道其具有(4)Δ基电子态)更是如此。在最初的理论研究中，发现随着动力学关联处理的改进，气相绝热(4)Δ←(6)Δ转变能急剧下降，最终结果表明FeCN((4)Δ)和FeNc((6)Δ)异构体具有不同的基电子态。(4)FeCN的Δ基态已得到实验验证。在这项工作中，使用耦合团簇理论直到完全四重激发(CCSDTQ)和大基组CCSDT计算的从头算复合方法与多参考组态相互作用(MRCI)能量进行了比较，其复杂程度远远高于2004年的研究[DeYonker等人]。J·化学。太棒了。2004、120、4726]。尽管过去十年在标量相对论效应的处理方面取得了进展，改进了铁基组，计算机处理能力也大幅提高，但多参考方法仍然无法找到FeCN的正确基态，大基组MRCISD+Q结果提供了定性较差的绝热(4)Δ←(6)Δ跃迁能量，误差近5,000厘米(-1)。耦合团簇理论加上CCSD(T)后的附加修正，产生了(4)ΔFeCN基态，而(6)Δ态的能量只高了306 cm(-1)。计算得到FeNc的基态电子态为(6)Δ，仅比(4)Δ态高45 cm(-1)，比FeNc(4)Δ激发态低741 cm(-1)。令人惊讶的是，额外的CCSDT核-价关联附加校正使FeNC跃迁能量向(4)Δ基态移动，(4)Δ←(6)ΔTe为227 cm(-1)。
Formidable multireference character is known to exist in the quartet states of the neutral radicals iron monocyanide (FeCN) and iron monoisocyanide (FeNC), even more so than the controversial FeH radical (which is now definitively known to have a (4)Δ ground electronic state). In the initial theoretical study, it was found that the gas phase adiabatic (4)Δ ← (6)Δ transition energy plummeted with improving treatment of dynamical correlation, and final results suggested that FeCN ((4)Δ) and FeNC ((6)Δ) isomers have different ground electronic states. The (4)Δ ground state for FeCN has been since verified experimentally. In this work, an ab initio composite method employing coupled cluster theory up to full quadruple excitations (CCSDTQ) and large basis set CCSDT computations is compared to multireference configuration interaction (MRCI) energies at a level of sophistication far superior to the 2004 study [ DeYonker et al. J. Chem. Phys. 2004 , 120 , 4726 ]. Despite advances in the treatment of scalar relativistic effects, improved iron basis sets, and massive increases in computer processing power over the past decade, multireference methodologies still fail to find the correct ground state for FeCN, with large basis set MRCISD+Q results providing a qualitatively poor adiabatic (4)Δ ← (6)Δ transition energy, in error by nearly 5000 cm(-1). Coupled cluster theory with post-CCSD(T) additive corrections produces the (4)Δ FeCN ground state, with the (6)Δ state only 306 cm(-1) higher in energy. The ground electronic state of FeNC is computed to be (6)Δ and is only 45 cm(-1) higher in energy than the (4)Δ FeCN state while it is 741 cm(-1) lower in energy than the FeNC (4)Δ excited state. Surprisingly, an additional CCSDT additive correction for core-valence correlation shifts the FeNC transition energy in favor of a (4)Δ ground state, with a (4)Δ ← (6)Δ Te of 227 cm(-1).