Dielectric properties and the ferroelectric transition of the Stockmayer-fluid via computer simulation

Abstract

We report extensive molecular dynamics simulations of the Stockmayer fluid near the transition to fluid ferroelectric ordering monitored via the divergence of the static dielectric constant. The dependence of the transition on dipole strength, μ², temperature, T, and system size is investigated. The results are compared to a large number of previous simulations in the literature. We find that the effective transition temperature T/(ρ μ²) ≈ 0.19 for ρ = 0.8 is a good estimate in the range of the other parameter values considered here. In addition, we study the local field in relation to the structure and dynamics of the liquid phase as a function of temperature, dipole strength and polarizability.

Notes

†There appears to be no compelling experimental evidence of a ferroelectric transition in molecular fluids as Hoye and Stell remark 3.

‡The interesting history of the Onsager equation in relation to Debye's equation is dicussed by Stell in 4 and Henry in 5.

§More precisely, the standard derivation of Debye's equation (cf. section 4.5 in 6) assumes that molecules in the immediate vicinity of the central molecule do not contribute to its local electric field. These molecules are therefore omitted and the cavity becomes much larger. However, the radius of the cavity is never specified because it does not enter into the final result. The entire argument, however, is lacking transparency and rigour.

†If for instance the r ⁻⁶ term in the Stockmayer potential is multiplied by a factor λ, then the gas–liquid critical temperature shifts proportional to λ² as simple rescaling shows 36.