A comprehensive comparison between thermodynamic perturbation theory and first-order mean spherical approximation: Based on discrete potentials with hard core

摘要: Abstract Using the TL (Tang and Lu, 1993) method, Ornstein-Zernike integral equation is solved perturbatively under mean spherical approximation ( MSA ) for fluid with potential consisting of a hard sphere plus square-well square-shoulder HS  +  SW SS to obtain first-order analytic expressions radial distribution function RDF ), second-order direct correlation function, semi-analytic common thermodynamic properties. A comprehensive comparison between high temperature series expansion HTSE third-, fifth- seventh-order performed over wide parameter range both model fluids by using corresponding “exact” Monte Carlo results as reference; although carried out up seventh-order, not first order considered fair from calculation complexity perspective. It found that performance dramatically model-dependent: target potentials go , (i) there dramatic dropping in calculating properties, especially excess internal energy constant volume heat capacity cannot be predicted even qualitatively correctly. (ii) One tendency noticed gets more reliable increasing temperatures dealing pressure, Helmholtz free energy, enthalpy chemical potential. (iii) Concerning disappointing it displays cases thermodynamics. (iv) In case model, solution shown quantitatively correct pressure if reduced are low 0.8. On other hand, less model-dependent; most models, improves third-order properties improvements very demonstrable capacity; limited cases, fifth-order only within lower density domain shows bit inadaptation higher domain.