抄録
The solid-liquid transition of molecular crystals is discussed. The intermolecular potential and the free volume are assumed to be, respectively, of the forms
φ(r)=4ε{(σ⁄r)12−(σ⁄r)6}, vf=b(r−σ)3.
The free energies of the regular lattice (solid-like state) are calculated. For an irregular lattice (liquid-like state), the distribution function 4πr2g(r) is assumed to be constant for ri(1−Δ)≤r≤ri(1+Δ), instead of the δ(r−ri) function, and the free volume is of the from b(r−σ)3+b′(rΔ)3, where Δ means the irregularity, and b and b′ are the constants.
The free energies of the both lattices are compared, and the first order transition can be obtained. The transition temperature, the volume change and the entropy of melting are in good agreement with those of observed values of argon.
