Path integral Monte Carlo study of hydrogen tunneling effect on dielectric properties of molecular crystal 5-Bromo-9-hydroxyphenalenone

Abstract

The dielectric properties of proton(H)–deuteron(D) mixed crystals of the hydrogen-bonded material 5-Bromo-9-hydroxyphenalenone are studied using a novel path integral Monte Carlo (PIMC) method that takes account of the dipole induction effect depending on the relative proton configurations in the surrounding molecules. The induced dipole is evaluated using the fragment molecular orbital method with electron correlation included by second-order Møller–Plesset perturbation theory and long-range corrected density functional theory. The results show a greater influence of CH⋯O intermolecular weak hydrogen bonding on the induction than for results evaluated with the Hartree–Fock method. The induction correction is incorporated into the PIMC simulations with a model Hamiltonian that consists of long-range dipolar interactions and a transverse term describing proton tunneling. The relationship between the calculated phase transition temperature and H/D mixing ratio is consistent with the experimental phase diagram, indicating that the balance between the proton tunneling and the collective ordering is appropriately described.