Molecular simulations are becoming now a days standard tools to investigate the behavior of several complex systems, including thermodynamic, structural and transport properties. In fact, simulations are used in some cases as alternative tools to search for the optimal conditions of a given process (phase separation, extraction, selectivity of one compound versus other) and even to guide the design of new materials and compounds. The great success of molecular simulations is due to several combined reasons: (1) the tremendous capacity of today computers, able to perform calculations unaffordable only few years ago, (2) the development of new algorithms to tackle different problems in an efficient manner and (3) the extension of these techniques to multidisciplinary fields. A complement to molecular simulations are molecular-based theories: they are constructed with the same underlying model, although some approximations are made in order to obtain an analytical equation. Although approximate, a main advantage of molecular-based equations versus molecular simulations is the speed of their calculations; in addition the accuracy of these equations can be assessed by direct comparison with molecular simulations for the same systems.

After an overview of some of the recent developments in the field we will concentrate here in the application of molecular simulations and theories to several problems of environmental interest, in particular: (1) thermodynamic, structural and transport properties of ionic liquids [1], (2) quantitative predictions of mixtures in the near critical region [2,3] and (3) simultaneous predictions of phase and interface properties by theory and simulations [4,5,6]. We will also address some of the limitations we face now a days when applying these techniques to some new problems, such as the need of more accurate force fields.

[1] C. Rey-Castro, L.F. Vega, submitted (2006)
[2] F. Llovell, J.C. Pàmies, L.F. Vega, J. Chem. Phys. 121, 10715 (2004)
[3] F. Llovell, L.F. Vega, J. Phys. Chem. B. 110, 1350 (2006)
[4] D. Duque, J.C. Pàmies, L.F. Vega, J. Chem. Phys. 121, 11395 (2004)
[5] A. Mejía, J.C. Pàmies, D. Duque, H. Segura, L.F. Vega, J. Chem. Phys. 123, 034505 (2005)
[6] A. Mejía, L.F. Vega, submitted (2006)