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首页> 外文期刊>International Journal of Quantum Chemistry >Direct (through-space) and indirect (through-bridge) components of the chemical bond multiplicities
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Direct (through-space) and indirect (through-bridge) components of the chemical bond multiplicities

机译：化学键多重性的直接（贯通空间）和间接（贯通桥）成分

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It is argued that the chemical bond concept embodies all types of dependencies between general basis functions, called "atomic orbitals" (AO), which are used to construct the bonding subspace of the occupied molecular orbitals (MOs), which in the single-determinant LCAO MO type approach fully describes the bonding pattern of a molecule. The chemical interaction between the specified AO can be both of the direct and indirect origin: the former results from the explicit dependency between the interacting AO, due to their constructive interference in a molecule, and the latter has its roots in the implicit dependencies between basis functions in the molecular bonding subspace. The indirect (through-bridge) contributions complement the familiar direct (through-space) bond-orders in the resultant pattern of bond multiplicities. The implicit components, realized via AO intermediates, are examined using the "quadratic" Wiberg approach to the localized bond-orders and their information sources are investigated in the orbital communication theory of the chemical bond, in terms of the cascade communications between AO. The explicit and implicit dependencies between basis functions in the bonding subspace are linked to the relevant elements of the molecular charge-and-bond-order matrix. The conditional probabilities of the direct and bridge (cascade) probability propagations ("communications") between AO, which determine the associated molecular information channels, are derived and used to determine the information-theoretic (IT) bond descriptors. These entropy/information indices of the bond covalency and ionicity accordingly reflect the average "noise" and the amount of the information flow in the molecular communications between AO. The multistage propagations involving full cascades of parallel AO bridges are shown to conserve the direct, stationary scattering probability between the given pair of terminal AO. This demonstrates the internal consistency of the bridge perspective on propagation of the electronic information in molecules. The associated Wiberg-type (quadratic) bond-order measures and IT bond multiplicities for these two types of interactions between AO are illustrated in the Hückel theory for selected π-electron systems (benzene, butadiene, and linear polyenes). In all these representative molecular systems, the resultant bond indices, combining the direct and indirect multiplicity contributions, are shown to generate a more balanced bonding perspective compared with the corresponding patterns resulting from the direct (Wiberg) bond-order approach alone. As illustrated for linear polyenes, the direct bonding can be realized at relatively short distances, while the indirect mechanism effectively extends the range of chemical interactions in molecular systems. The AO-resolved communications have been examined in a general basis set case, and the "transition" communication system for the "promolecule" → molecule transformation has been proposed.
机译：有人认为，化学键的概念体现了被称为“原子轨道”（AO）的通用基函数之间的所有类型的依存关系，它们被用来构建占据分子轨道（MOs）的键合子空间，该空间在单行列式中LCAO MO类型方法充分描述了分子的键合模式。指定的AO之间的化学相互作用可以是直接的也可以是间接的：前者是由于相互作用的AO在分子中的结构性干涉而引起的，而后者的根源在于基础之间的隐性依赖。在分子键合子空间中起作用。间接的（直通桥）贡献以键合多重性的结果模式补充了熟悉的直接（直通空间）键序。通过“二次” Wiberg方法对局部键序进行检查，通过AO中间体实现的隐式成分，并根据AO之间的级联通信，在化学键的轨道通信理论中研究了其信息源。键子空间中基本函数之间的显式和隐式相关性链接到分子电荷键顺序矩阵的相关元素。推导确定关联分子信息通道的AO之间直接和桥接（级联）概率传播（“通信”）的条件概率，并将其用于确定信息理论（IT）键描述符。这些键共价和离子性的熵/信息指数相应地反映了AO之间分子通信中的平均“噪声”和信息流的量。涉及并行AO桥的完整级联的多级传播被显示为保留给定的一对AO端之间的直接，静态散射概率。这证明了电子分子中分子信息传播的桥梁观点的内部一致性。针对选定的π电子体系（苯，丁二烯和线性多烯）的Hückel理论说明了AO之间这两种相互作用类型的相关Wiberg型（二次）键序量度和IT键多重性。在所有这些代表性的分子系统中，与直接（Wiberg）键序方法单独产生的相应模式相比，结合直接和间接多重贡献的所得键指数显示出更加平衡的键视角。如线性多烯所示，直接键合可以在相对较短的距离上实现，而间接机制则有效地扩展了分子系统中化学相互作用的范围。已在一般的基础情况下检查了AO解决的通信，并提出了用于“前大分子”→“分子转化”的“过渡”通信系统。

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