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Fe_2S_2(SH_4~(2-))或Fe_2S_2Cl_4~(2-)离子是铁硫蛋白的2Fe原子簇模型分子,借助其电子结构的实验和理论研究,有利于阐明铁硫蛋白氧化还原反应的电子传递。对它们所作的许多量化计算,主要是半经验EHMO方法和SCF-SW-X_α方法。所得结论大体相同,即前沿占有分子轨道以Fe3d原子轨道为主要成份,桥S原子对成键起重要(或主要)作用。但非限制性SCF-SW-X_α-VB方法的结果有所不同:Fe 3d分子轨道位于较低能级区,前沿分子轨道以S、Cl的孤对轨道为主要成份。这种分歧吸引我们用第三种方法——单行列式从头计算进行研究,虽然这种方法也存在某种争议。
Fe_2S_2 (SH_4 ~ (2-)) or Fe_2S_2Cl_4 ~ (2-) ions are the 2Fe cluster model molecules of iron-sulfur protein. With the help of their electronic structure experimental and theoretical studies, it is helpful to elucidate the electron transfer of iron-sulfur protein redox reaction . Many of the quantitative calculations they make are mainly the semi-empirical EHMO method and the SCF-SW-Xα method. The conclusions are roughly the same, that is, the frontier occupied molecular orbital with Fe3d atomic orbit as the main component, bridge S atoms on the bond plays an important (or main) role. However, the results of the non-limiting SCF-SW-X_α-VB method are different: the Fe 3d molecular orbital is located in the lower energy level region, and the leading molecular orbital is dominated by the orbital pair of S and Cl. This disagreement has drawn us to a third-of-all-measure, ab initio study, although there is some controversy with this approach.