镧系元素4f轨道在成键中的作用的理论研究  

Theoretical Study on the Role of Lanthanide 4f Orbitals in Bonding

作　　者：王繁[1] 黎乐民[1] 

机构地区：[1]北京大学化学与分子工程学院

出　　处：《化学学报》2002年第8期1379-1384,共6页Acta Chimica Sinica

基　　金：国家自然科学基金 (Nos.2 9892 163 ;2 992 80 0 2 )

摘　　要：用密度泛函方法在冻结或不冻结 4f轨道的条件下计算一系列含镧系元素双原子分子 ,对结果进行分析 ,得出以下结论 :镧系元素 4f轨道按传统的化学键理论观点是不直接参与成键的 ,但对成键有一定作用 :通过与匹配物的轨道混合使键长变短 ,键能增加 ,一般可达百分之几 .随着镧系原子序数的增加 4f轨道对成键的贡献减少 .电负性高或价态高的匹配物对 4f轨道的作用较强 ,4f轨道对成键的影响比较大 .对于重镧系元素 ,匹配物不是F或O时 ,4f轨道对成键的贡献相当小 ,可以看成芯轨道 ,但对于轻稀土 ,在比较精确的计算中则应作为价轨道处理 .镧系元素与氟结合时 ,只有对靠近Yb的重镧系元素才可以把 4f当作芯轨道 。A series of diatomic molecules containing lanthanides (Ln) are studied by means of density functional calculations with or without the In 4f orbitals frozen. Based on analysis of the calculated results the following can be concluded. The Ln 4f orbitals do not directly participate in bonding from the view-point of traditional bonding theory, but may influence the bonding to a certain extent through mixing a little match orbitals into the localized 4f orbitals and mixing some 4f component into the delocalized molecular orbitals, causing the bond lengths shortened and the bonding energy increased by about several hundredths in general. The contribution of 4f orbitals lessens with the increase of the atomic number of lanthanides. The matches with higher electronegativity or higher valences act on the 4f orbitals more strongly, resulting in larger influence of the 4f orbitals on bonding. Except for the matches being F or 0, the 4f orbitals contribute to bonding quite small for the heavy lanthanides, and they can be considered as core orbitals, but they should be considered as valence orbitals in accurate calculations for the light lanthanides. In lanthanide fluorides the 4f orbitals can be treated as core orbitals only for the heavier lanthanides near Yb, while in lanthanide oxides sensible errors may occur if the 4f orbitals are dealt with as core orbitals even for YbO.

关 键 词：理论研究 镧系元素 4F轨道 化学键 密度泛函理论 成键作用 

分 类 号：O641[理学—物理化学]