The study of H/D isotope‐dependent order–disorder transition in crystalline α‐chromous acid using quantum‐chemical modeling

Abstract

Abstract The ferroelectric behavior of the protonated (HCrO 2 ) and deuterated (DCrO 2 ) forms of the crystalline α‐chromous acid is studied by quantum‐chemical evaluation of the dynamic Ising model parameters. The tunneling parameters Ω(H), Ω(D) were found from proton transfer barriers calculated by various techniques including the fourth‐order Møller‐Plesset perturbation theory and coupled cluster schemes. The Ising parameters J ij (H), J ij (D) as well as the molecular field parameters J 0 (H), J 0 (D) were obtained in frames of two‐pseudospin cluster method on the same computational levels. The molecular field approach was applied to the problem of the structural phase transition (SPT) existence. It is shown in an agreement with experimental data that α‐HCrO 2 cannot undergo the SPT related to the ordering of its proton subsystem. On the contrary, the SPT of this sort, that is antiferroelectric in character, takes place in α‐DCrO 2 due to strong geometric H/D‐isotope effect observed. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007