Perturbational molecular orbital (MO) theory has been one of the key components in understanding electronic structures and chemical bonding based on orbital interactions.  The interest lies in seeing how the energy levels of molecules and solids are altered electronically during a perturbation involving molecular assembly, geometrical change, or atomic substitution.  Herein we present an extension of the method for understanding of spin polarized molecules and solids by using “spin polarization” as a perturbation within density functional formalism.  We show how the new approach can unify the seemingly isolated concepts of magnetic interactions in metallic, covalent and ionic systems.  With some examples, we present spin polarization as a versatile alternative concept for studies of covalent magnetism and illustrate how chemical bonding in metallic compounds influence their magnetism.  Connections are made among the concepts of Stoner condition for ferromagnetism in metals, magnetic exchange interactions in Mott-Hubbard insulators, Ruderman-Kittel-Kasuya-Yosida interactions in rare earth metals, McConnell mechanism for spin polarization in radicals and magnetic interactions in organic compounds.  It is shown that all these concepts can be understood within the new formalism by analyzing and predicting how an initial spin polarization in an electronic system can induce additional spin polarization that spatially propagates through covalent bonds.<br/>

Density functional perturbational orbital approach in understanding of covalent magnetism through chemical bonds

254th National Meeting (2017)

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