Abstract: On the basis of the density functional theory of grand canonical ensembles, the definition on electronegative and hardness of atoms and molecules proposed by Parr are extended to molecular fragment chemistry. Energy E(N) versus △N curves for certain transition metal carbonylmetallates are calculated by using density functional theory at the local density approximation(LDA) level and at the LDA/NL level with further non-local corrections for exchange and correlation included self-consistently. It is shown that the energy curve of the molecular fragments is convex. In general, derivative discontinuities of the energy at integral electron number N are found. Therefore the finite-difference method is used in calculation on the electronegative and hardness of the molecular fragments. It is revealed from the calculated results for certain typical compounds that the calculated electronegative and hardness are reasonably in agreement with Pearson's values. On the basis of the calculated electronegative and hardness, relative acidities for HMn(CO)₅, [HFe(CO)₅]⁺, H₂Fe(CO) and HCo(CO)₄ are explained reasonably, and mechanisms of substitution reactions between [Mn(CO)₅] and Cr(CO)₅, as well as between Co(CO)₄^- and Fe(CO)₅ are in detail discussed. It is shown from our calculations that chemical properties of the molecular fragments may be characterized by the electronegative and hardness of density functional theory.

Key words: molecular fragment, density functional theory, electronegative, hardness

摘要： 在巨正则系综的密度泛函理论基础上，把Parr等人提出的原子与分子体系的电负性与硬度的定义应用到分子片化学中，并应用密度泛函理论最新发展的 DFT-LDA/NL方法计算了一些过渡金属羰基分子片的E(N)—ΔN能量曲线。结果表明，分子片的能量函数E(N)是凸函数。但是，在一般情况下，在整数电荷处出现导数不连续。因此有限差分近似被应用于分子片的电负性与硬度的具体计算。通过对典型化合物的计算表明，有限差分法的计算结果是合理的，与Pearson的实验值接近。应用DFT-LDA/NL计算的电负性与硬度，解释了HMn(CO)₅，[HFe(CO)₅]⁺，H₂Fe(CO)₄和HCo(CO)₄的相对酸性；分析了 [Mn(CO)₅]^-与Cr(CO)₅, Co(CO)₄^-与Fe(CO)₅之间的分子片取代反应的可能路径。研究表明可以应用密度泛函理论定义的电负性与硬度，从理论上来表征分子片的化学性质。

关键词: 分子片化学, 密度泛函, 电负性, 硬度