Density functional theory for calculating surface tensions with a simple renormalization formalism for the critical point

The calculation of interfacial properties, such as the surface tension, from the density functional theory suffers from the overestimation of the critical temperature of all classical Helmholtz energy functionals. A Helmholtz energy functional is here proposed, where the long-range density fluctuations leading to the universal critical scaling behavior are accounted for using a renormalization group theory. The appeal of the approach is its simple implementation, where the renormalization is treated in a local density approximation (LDA). The model is almost exact at the critical point. Away from the critical point, the model reduces to the perturbed chain statistical associated fluid theory (PC-SAFT) equation of state. The conventional PC-SAFT pure component parameters are supplemented with a single substance-specific renormalization parameter, which is adjusted to reproduce the bulk phase critical temperature. The surface tension is obtained with excellent agreement to experimental data for some non-polar and moderately polar substances (alkanes, ethers, acetates and aromatic substances) up to the critical point.