This study uses theoretically methods to investigate, for metal diiodides MI₂ (M = Mg, Ca, Mn, Fe, Cd, Pb) with CdI₂ (2H polytype) structure, the mutual correlation between the structure‐characterizing parameters (the flatness parameter of monolayers f, the Madelung constant A, and bonding angle I—M—I) and correlation of these parameters with contributions of the Coulomb and covalent energies to cohesive energy. The energy contributions to cohesive energy are determined with the use of empirical atomic potentials. It is demonstrated that the parameters f and A, and the bonding angle I—M—I are strictly correlated and increase in the same order: FeI₂ < PbI₂ < MnI₂ < CdI₂ < MgI₂ < CaI₂. It is found that with an increase of parameter A and bonding angle I—M—I the relative contribution of the Coulomb energy to cohesive energy increases, whereas the relative contribution of the covalent energy decreases. For a hypothetical MX₂ layered compound with the CdI₂ (2H polytype) structure, composed of regular MX₆ octahedra (angle X—M—X = 90°), the flatness parameter and the Madelung constant are found to be f_reg = 2.449 and A_reg = 2.183, respectively. Correlation of the covalent energy with the type of distortion of MI₆ octahedra (elongation or compression) with respect to regular configuration (angle I—M—I = 90°) is also analyzed.

中文翻译：

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具有CdI2（2H多型）结构的层状金属二碘化物（MI2）中马德隆常数和I-M-I键角与内聚能贡献的相关性

本研究使用理论方法研究 具有CdI ₂（2H多型）结构的金属二碘化物M I ₂（M = Mg，Ca，Mn，Fe，Cd，Pb）的结构特征参数之间的相互关系（平坦度）单层参数f，马德隆常数A和键角MM）以及这些参数与库仑和共价能对内聚能的关系。能量对内聚能的贡献是通过经验原子势来确定的。据表明，参数˚F和甲，和接合角I-中号-I严格相关，并且增加以相同的顺序：费₂ <碘化铅₂ <MNI ₂ <CDI ₂ <MGI ₂ <了Cal ₂。据发现，随着参数的阿和接合角I-中号-I库仑能量到内聚能量增加的相对贡献，而共价能量的相对贡献降低。对于具有CdI ₂（2H多型）结构的假设MX ₂层状化合物，它由规则的MX ₆八面体（角X — M — X= 90°），平坦度参数和Madelung常数分别为f _reg = 2.449和A _reg = 2.183。还分析了共价能与M I ₆八面体的畸变类型（伸长或压缩）相对于规则构型（角度I M = = 90°）的相关性。