The Unrestricted Hartree-Fock Theory of Chemical Reactions. IV: Singlet Radical States with “Antiferromagnetic” Spin Orderings in Four-Center Exchange Reaction of Hydrogen Molecules
The Unrestricted Hartree-Fock Theory of Chemical Reactions. IV: Singlet Radical States with “Antiferromagnetic” Spin Orderings in Four-Center Exchange Reaction of Hydrogen Molecules
复制标题
化学反应的无限制 Hartree-Fock 理论 IV：氢分子四中心交换反应中具有“反铁磁”自旋有序的单线态自由基态。
DOI：
10.1143/ptp.53.1580
复制
发表时间：
1975
影响因子：
--
通讯作者：
T. Takabe
中科院分区：
文献类型：
--
作者：
H. Fukutome;Mitsuo Takahashi;T. Takabe
对反应路径上的两个氢分子与D.对称性包括D.，，D ··和T，confor.作为特殊情况。结果表明，H.系统由十个不同的UHF组态组成，它们出现在核组态空间的不同区域。十种构型中有三种是闭壳型的，另外七种对应于具有不同的“反铁磁”有序自旋结构的单重态自由基。七个单重态自由基组态中的三个具有一维调制的自旋结构，另外三个具有二维调制的自旋结构，并且非常类似于Overhauser的螺旋自旋密度波。另一种构型具有四面体调制的自旋艾德结构。计算了UHF组态的绝热势，研究了它们的互连关系。这些单重态自由基的电子相关效应进行了讨论与轨道相关图。第一节在以前的论文中，我们讨论了非限制性Hartree-Fock（UHF）理论中不稳定性和对称性破缺解的化学意义，并证明了单重态双自由基的电子态可以很好地用自旋密度波（SDW）型解来表示，这种解是由限制性Hartree-Fock（RHF）解的不稳定性产生的。本文考虑了具有D2对称性构象的两个氢分子的四中心交换反应，其中包括具有D2 h，D2 rt和Trt对称性构象的两个氢分子的四中心交换反应。·我们将从H4体系的详细UHF理论分析中表明，存在具有比具有两个未成对电子的简单双自由基更复杂的电子结构的单线态自由基。H4体系在过渡构象附近可以进入7种不同的单重自由基态，这些单重自由基态具有不同的“反铁磁”自旋结构.其中三个类似于Uiwdin，5l Itoh和Yoshizumi的交替轨道，6l，另外三个类似于Overhauser 7 l的螺旋SDW，另一个具有以三维方式调制的自旋结构。在反应分子体系中存在如此丰富的单重态自由基及其相互转化的可能性，
A UHF theoretical analysis is carried out on four-center exchange reaction of two hydrogen molecules in reaction paths with D. symmetry including D.,, D •• and T, confor. mations as special cases. It is shown that the UHF singlet ground state of the H. system consists of ten distinct UHF configurations which appear at different regions of nuclear con figuration space. Three among the ten configurations are closed shell type and the other seven correspond to singlet radicals with distinct "antiferromagnetically" ordered spin structures. Three among the seven singlet radical configurations have spin structures modulated one dimensionally, the other three have those modulated two dimensionally and are very similar to Overhauser's helical spin density wave. Another configuration has tetra-hedrally modulat ed spin structure. The adiabatic potentials of the UHF configurations are calculated and their interconnection relation is studied. The electronic correlation effects underlying these singlet radical states are discussed in connection with orbital co;rrelation diagrams. · § I. Introduction In previous papers/>-'> we have discussed chemical significances of the instabilities and the broken symmetry solutions in the unrestricted Hartree-F.ock (UHF) theory and shown· that the electronic state of a singlet biradical can be well represented by a spin density wave (SDW) type solution which emerges from an instability of a restricted Hartree-Fock (RHF) solution. We consider, in this paper, the four-center exchange reaction of two hydrogen molecules in the conformations with D 2 symmetry including those with D2h, D 2rt and Trt symmetries as special cases. · We shall show from a detailed UHF theoretical analysis of the H 4 system that there are singlet radicals with more complex electronic structures than the simple biradicals with two unpaired electrons. The H 4 system may enter into seven different singlet radical states, which· are characterized by distinct "antiferromagnetic" spin structures, in the regions near the transition conformations. Three of them are similar to the alternant orbital of Uiwdin,5l Itoh and Yoshizumi,6l the other three to the helical SDW of Overhauser 7l and another one has a spin structure modulated in a three-dimensional way. Possibility of such plentiful kinds of singlet radicals and their interconversion in reacting molecular systems has not been recognized so