Methodological approaches for the free energy calculations in electroactive SAMs

Abstract

We compare the Free Energy Perturbation (FEP) and Thermodynamic Integration (TI) approaches in slab-geometries where the electrostatic interactions are handled with the standard three-dimensionally Ewald summation technique. The comparison between FEP and TI is made through energy distributions in the analysis of the phase space sampling between the forward and backward directions, the reversibility of the perturbation, the number of windows and the consistency of the free energy decomposition into individual components. We report here free energy calculations in order to predict the shift in the redox potential in self-assembled monolayers (SAMs) as the coadsorbed chain length is changed. The reproduction of the free energies with respect to the electrolyte is tested on neutral and charged simulation cells.

Keywords:

• electroactive self-assembled monolayers
• molecular dynamics
• free energy calculations
• TI
• FEP

Acknowledgement

This work was granted access to the HPC resources of IDRIS under the allocation 2011-i2009092119 made by GENCI (Grand Equipement National de Calcul Intensif).