Complex pole approach in thermodynamic description of fluid mixtures with small number of molecules

•Behavior of gas–liquid mixtures with small number of molecules in finite volume.•The analysis is performed in the frame of equilibrium statistical physics.•Partition function is evaluated by complex pole method.•Previous one-component method is extended for multicomponent molecular mixtures.•Size dependent additional pressure for small systems is computed.

The subject matter of classical thermodynamics is the asymptotic behavior of equilibrium systems in thermodynamic limit, for small molecular systems, when transition to thermodynamic limit is impossible, the extension of thermodynamics is required. This work studies novel approach for the evaluation of partition functions of small systems by complex pole analysis. Several cases for molecular systems in small cavities are studied numerically. In particular size-dependent additional pressure for small systems is evaluated analytically and numerically. Similar approach was developed earlier in nuclear physics for finite systems of nucleons. The obtained results correspond to published experimental data and molecular dynamics simulations.