Alkali halides arehalideF center in halide crystal is a negative ion vacancy that captures aElectronicsF center electrons are bound to the ion vacancy under the action of the potential field formed by the surrounding ions.
In 1998, the Nobel Prize in Chemistry was awarded to Walter Kohn, who proposed density functional theory, and John Pople, who proposed computational chemistry, which announced the end of "chemistry is only experimental science" and the era of "experiment and formal theory are both the two pillars of chemistry" has come.Therefore, Academician Xu Guangxian listed "molecular structure and its quantitative relationship with performance" as one of the "four century problems" of chemistry in the 21st century in his article on "structural chemistry"Structural chemistryAnd even one of the main research contents of the whole chemistry.According to a basic law of chemistry, "structure determines performance, and performance reflects structure", so there must be a close correlation between structure and performance.Most of them describe this relationship qualitatively, but fail to make quantitative inference.The reason is that the abstract molecular structure cannot be numerically characterized.For this, althoughquantum chemistryAlthough remarkable achievements have been made, the calculation method is too complicated and only suitable for a few small molecules.How to easily generate the numerical values of different molecular structures and achieve unique characterization is the first key to explore the "quantitative relationship between structure and performance".The second key is that the value derived from the molecular structure should be significantly related to the corresponding performance.In order to achieve this goal, chemists have made unremitting exploration and proposed a variety of numerical characterization methods for molecular structures.Among them, the topological index method is the most simple and effective.This article is based on the molecular topology theoryatomThe characteristic connectivity index (mF), whose first order index (1F) not only uniquely characterizes the structure of inorganic molecules, but also combines with the F center energy band [E (F)], lattice energy (U), standardentropy(Sm θ) and other properties show a good quantitative relationship.
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1. Under the same alkali metal condition, the ionic property of M-X bond decreases in the order of F, Cl, Br, I, and the corresponding 1F decreases;
2. Under the same halogen condition, 1F decreases with the decrease of electronegativity of Li, Na, K, Rb, Cs.This trend is consistent with the law of E (F);
3. The other factor affecting E (F) is the mass of the bonding atom (m, which should be the sum of the mass of M and X atoms).The larger the m, the larger the corresponding atomic radius (the smaller the electronegativity), and the larger the bond length R, resulting in the lower E (F).[1]
