Quantum Chemistry in Position Space and Chemical Bonding in Intermetallic Compounds

Intermetallic compounds are formed by elements located left from the Zintl line in the Periodic Table. For interpretation of their chemical and physical properties a better understanding of the chemical composition and bonding in crystal structures of these substances is necessary. Especially the chemical bonding in intermetallic compounds is a rather open question [1]. An application of new quantum-chemical tools in real space like the electron localizability approach [2-5] opens the way to real-space definition of the basic categories for chemical bonding description like covalence or ionicity [6] or polarity [7]. On that base, the Pauling‘s 8–N rule is re-defined for the real space and used for a consistent and quantitative treatment of heteropolar bonding situations exemplarily for compounds of the MgAgAs type and their relatives [8]. The QTAIM Madelung energy calculated using effective charges and the exchange energy obtained by point-charge approximation from the delocalization indexes were used to identify favourable element combinations for new MgAgAs-type compounds. Two so-predicted high-temperature phases VIrGe and the low-temperature modification of HfPtGe showing this type of crystal structure were prepared and characterized [9]. Furthermore, the electron localizability approach allows to study even the weak van-der-Waals bonding [10] and visualize the multi-centre interactions [11].

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