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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Physical Understanding through Variational Reasoning: Electron Sharing and Covalent Bonding
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Physical Understanding through Variational Reasoning: Electron Sharing and Covalent Bonding

机译：通过变分推理的物理理解：电子共享和共价键

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摘要

Energy changes of stationary states resulting from geometric parameter changes in the Hamiltonian can be understood by variational reasoning in terms of the physical attributes of the kinetic and the potential energy functionals. In atoms as well as molecules, the energy minimization determines the ground state as the optimal compromise between the potential pull of the nuclear attractions and the localization-resisting kinetic pressure of the electron cloud. This variational competition is analyzed for the exact ab initio ground-state wave function of the hydrogen molecule ion to elucidate the formation of the bond. Its electronic wave function is shown to differ from the ground-state wave function of the hydrogen atom by polarization, sharing, and contraction, and the corresponding contributions to the binding energy are examined in detail. All told, the critical feature is that a molecular orbital, contracting (in the variational context) toward two nuclei simultaneously, can lower its potential energy while maintaining a certain degree of delocalization. As a consequence, its kinetic energy functional has a lower value than that of an orbital contracting toward a single nucleus equally closely. By contrast, the potential energy functional is lowered equally effectively whether the orbital contracts toward one nucleus or simultaneously toward two nuclei. Because of this weaker kinetic energy pressure, the electrostatic potential pull of the nuclei in the molecule is able to attach the orbital more tightly to each of the nuclei than the pull of the single nucleus in the atom is able to do. The role of the virial theorem is clarified. Generalizations to other molecules are discussed.
机译：由汉密尔顿方程中的几何参数变化导致的稳态能量变化可以通过动量和势能函数的物理属性的变分推理来理解。在原子以及分子中，能量最小化将基态确定为核引力的潜在吸引力和电子云的抗局部化动压之间的最佳折衷。针对氢分子离子的精确的从头算起的基态波函数，分析了这种变分竞争，以阐明键的形成。它的电子波函数通过极化，共享和收缩显示出不同于氢原子的基态波函数，并详细研究了其对结合能的贡献。总而言之，关键特征是同时向两个原子核收缩的分子轨道（在变体环境中）可以降低其势能，同时保持一定程度的离域化。结果，它的动能泛函的值比同等程度地朝单个核收缩的轨道的动能泛函的值低。相比之下，无论轨道朝向一个核收缩还是同时朝向两个核收缩，势能函数均有效地降低。由于这种较弱的动能压力，分子中原子核的静电势能比原子中单个原子核的能动性更强地将轨道连接到每个原子核上。阐明了维里定理的作用。讨论了对其他分子的概括。

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