Abstract: A method is proposed to construct a localized active functional space from the density matrix of a large system. The large system is partitioned into central and surrounding areas. The active functional space is mainly localized on the central area. It contains all basis functions centered at the central area and all the orbitals which consist of the basis functions localized in the surrounding area and interact with the basis functions in the central area to a certain extent. An integral number of electrons are involved in the localized active functional space which can be considered as a relatively independent subsystem in the large system and for which formally isolated quantum chemical calculations can be performed. The related program has been coded and is checked through calculating the number of 4f electrons involved in the active functional space centered in the lanthanide atom of lanthanide trichloride and hydrated lanthanide ions.

Key words: density matrix, localized active functional space, program

摘要： 报道了从大体系的密度矩阵出发构造定域于指定局部的活性泛函空间的方法和程序。将大体系划分为中心区和环境区，活性泛函空间包含中心区的基函数及与其有相互作用的环境区轨道，容纳整数个电子，构成大体系的一个相对独立的子体系，可以在其中进行独立的量子化学计算。通过计算镧系氯化物和水合离子的4f电子数等对所编程序进行了验证。

关键词: 密度矩阵, 局域活性泛函空间, 程序