Abstract

First the applications of angular and oscillatory radial forces that are derived quantum mechanically for metals are reviewed, emphasizing the μ4 methods of generating angular forces. The dominant conclusion from several applications that are discussed is that bcc transition metals will often sacrifice bond-length constraints in order to obtain an energetically favorable angular environment. Then the derivation of angular and torsional forces for polymers such as proteins, in which chemical bonds remain fairly intact, are discussed. The derivation of the iμ4 methodology is briefly reviewed, and it is shown that the earlier μ4 analysis of the angular forces can be understood in terms of overlap repulsion between bond orbitals. This overlap repulsion is used to develop simplified forms for angular interactions in well-bonded systems. These angular interactions are consistent with the structures of P and S. A result of this analysis is that some of the "improper" torsion terms that are typically used in polymer simulations may be unnecessary. It is then shown that torsional forces in polymers can be understood by a second-order perturbation analysis, in which one takes into account the interaction between hybridized bond orbitals on one atom with hybridized antibond orbitals on other atoms. The resulting torsional forces are consistent with the structures of elemental S and the ethane molecule.

Original languageEnglish
Pages (from-to)608-613
Number of pages6
JournalJournal of Phase Equilibria
Volume18
Issue number6
DOIs
StatePublished - Dec 1997

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