Improved analytical thermodynamic properties of the triangular-well fluid from perturbation theory

► The triangular-well fluid equation of state is improved. ► The equation of state is analytical without many numerical coefficients. ► The analytical 2nd order term of the free energy is in agreement with the numerical Barker-Henderson perturbation term. ► The residual internal energy and reduced pressure are in agreement with Monte Carlo results for short-range potentials.