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Keywords:

  • strong hydrogen bonds;
  • H-bonded solids;
  • quantum–chemical modeling

Abstract

To describe the proton–phonon coupling (PPC) in the materials at hand, the novel pseudospin Ising-type Hamiltonian is proposed. It is derived by the vibronic theory of heteroligand molecular systems treating the oxygen atoms O(−) and O(···) [linked with hydrogen atoms by covalent (O[BOND]H) or by hydrogen (O···H) bond] as substituting ligands in PO4 tetrahedra for 3d KH2PO4-like species. Using the Hamiltonian obtained, we treat several vibrational modes participating in the structural phase transitions, the Ising parameters dependence on vibronic constants, and the PPC influence on the Tc value. © 2012 Wiley Periodicals, Inc.