Density functional approximation for van der Waals fluids： based on hard sphere density functional approximation

A universal theoretical approach is proposed which enables all hardsphere density functional approximations (DFAs) applicable to van derWaals fluids. The resultant DFA obtained by combining the universaltheoretical approach with any hard sphere DFAs only needs as input asecond-order direct correlation function (DCF) of a coexistence bulkfluid, and is applicable in both supercritical and subcriticaltemperature regions. The associated effective hard sphere density canbe specified by a hard wall sum rule. It is indicated that the valueof the effective hard sphere density so determined can be universal,i.e. can be applied to any external potentials different from thesingle hard wall. As an illustrating example, the universaltheoretical approach is combined with a hard sphere bridge DFA topredict the density profile of a hard core attractive Yukawa modelfluid influenced by diverse external fields; agreement between thepresent formalism's predictions and the corresponding simulation datais good or at least comparable to several previous DFT approaches.The primary advantage of the present theoretical approach combinedwith other hard sphere DFAs is discussed.

Density functional approximation for van der Waals fluids: based on hard sphere density functional approximation

A universal theoretical approach is proposed which enables all hardsphere density functional approximations (DFAs) applicable to van derWaals fluids. The resultant DFA obtained by combining the universaltheoretical approach with any hard sphere DFAs only needs as input asecond-order direct correlation function (DCF) of a coexistence bulkfluid, and is applicable in both supercritical and subcriticaltemperature regions. The associated effective hard sphere density canbe specified by a hard wall sum rule. It is indicated that the valueof the effective hard sphere density so determined can be universal,i.e. can be applied to any external potentials different from thesingle hard wall. As an illustrating example, the universaltheoretical approach is combined with a hard sphere bridge DFA topredict the density profile of a hard core attractive Yukawa modelfluid influenced by diverse external fields; agreement between thepresent formalism's predictions and the corresponding simulation datais good or at least comparable to several previous DFT approaches.The primary advantage of the present theoretical approach combinedwith other hard sphere DFAs is discussed.