# Phase equilibria of fluid mixtures via integral equations

*By Francesco
Colonna*

"Extraction, adsorption, distillation [...] are essential unit operation in chemical industry and an understanding of any of them is based, at least in part, on the science of phase equilibrium" ( Prausnitz et al.). Unfortunately, to predict a phase equilibrium is usually very hard and time-expensive. With the group of Prof. G. Pastore, we investigated the possibility of using the so-called "integral equations theory" of fluids to calculate the phase diagram of binary mixtures. We show that the "constant pressure integral equation approach" is a handy tool to calculate the phase equilibria of symmetric and asymmetric mixtures of fluids.

## Publications

- Fluid-phase diagrams of binary mixtures from constant pressure integral equations J. Chem. Phys. 122 (2005), 181104, DOI: 10.1063/1.1915347

# Accurate free energies from replica-exchange simulations

Hamiltonian replica-exchange is a simulation technique
used to improve the sampling of chemical and biological
systems with a complex free energy landscape. To be able to
calculate the absolute free energy difference between
different replicas, would allow us to use
Hamiltonian-replica exchange as a tool to estimate total
free energy differences, offering a promising alternative
to methods like
thermodynamic integration ,
Zwanzig's perturbation equation , and
lambda-dynamics.

To this end, we are developing a
stochastic technique that combines replica-exchange
simulations with free energy calculations.

# Multireference thermodynamic integration

Thermodynamic integration is a popular technique to compute the free energy of solids and fluids. In the case of layered systems, such as graphite, serious numerical difficulties appear, due to the possible movement of the layers in the solid, at least in the finite-size models used in computer simulations. To overcome this problem, we proposed a multireference simulation approach, showing how to construct the relative statistical ensemble, and how to calculate the free energies of the layered solids.