Abstract: The electronic structure and chemical bonding of Eu₂S and EuS₂ have been studied by means of the density functional theory. It is shown that the Eu-S bonding mainly comes from the interaction between Eu 5d and S 3p orbitals in both molecules. The 4f orbitals are localized in essence. The contribution of the Eu atomic orbitals to the Eu-S bonding follows the order: 5d>6p>6s>4f. The characteristics of the electronic structure show that the valence of Eu is 2 both in Eu₂S and EuS₂, which shows that the 4f orbitals can not become the signifacant component of the bonding molecular orbitals. The covalency of the Eu-S bond is 68% in Eu₂S and 57% in EuS₂.

Key words: Eu₂S, EuS₂, density functional theory, electronic structure, chemical bonding

摘要： 利用密度泛函理论方法(DFT)对Eu₂S, EuS₂的电子结构和化学键进行了研究。结果表明：Eu₂S和EuS₂分子中的Eu-S键均主要来自Eu 5d和S 3p轨道的相互作用，4f轨道基本上是定域的，Eu原子轨道对Eu-S键的贡献大小顺序均为5d>6p>6s>4f。电子结构特征表明，在Eu₂S和EuS₂中，Eu均保持为2价，4f轨道不能成为成键轨道的主要成分；Eu-S键的共价性成分分别为68%和57%。

关键词: Eu₂S, EuS₂, 密度泛函理论, 电子结构, 化学键