Advances in the Implementation of Polarizable Force Fields for Molecular Simulations
CECAM-HQ-EPFL, Lausanne, Switzerland
A potential energy function has to incorporate information about the system it describes. Much effort has been put into improving intermolecular potentials by refining simple models. This includes the representation of molecules as collections of atom-centered interaction sites with fixed partial charges; since the charges are fixed, there is no explicit treatment of electronic polarization, and intermolecular interactions are treated as pairwise additive. Though the impact of this approximation is diminished through the use of effective pair potentials with enhanced charges, the lack of explicit polarization is physically incorrect [2,3] and is well-known to be problematic for interactions with charge concentrated ions, interactions of ions with pi-electron systems, and even for less obvious cases such as polar solutes in low-dielectric media [4-8]. Nevertheless, after 30 years and universal agreement on the importance of the problem, generally accepted, broadly applicable polarizable force fields have not emerged, multiple treatments of polarizability (inducible dipoles, fluctuating charges, Drude oscillators, etc.) remain under consideration, and simulations of extended inhomogeneous systems with polarizable force fields are still uncommon. Recently, given the urge for more realistic descriptions in computer simulations [5,8-11], and thanks to the increased computational power, the activity in the field is knowing a renovated enthusiasm; studies with polarizable force fields are being performed in different areas of research such as liquid-air interfaces [6,7], water-salt solutions [4,5,12-14], liquid water [14,15] (its properties in ‘exotic’ conditions are still unknown), ionic liquids , cell membranes  and molten salts [14,18]. Nonetheless, it seems that development and thorough testing of a polarizable force field is still limited to a small niche of researchers, and that its spread to a wider simulation community is somehow damped by myriad applications of nonpolarizable force fields in modeling complex systems. In the medium and long term the impact and prospective capabilities of the simulation work will be affected by the quality of the underlying description of molecular energetics [2,3]. In this atmosphere, it was decided to gather the researchers to focus on current research on polarizability and polarizable force fields and to boost its applications, from molecular biology to medicinal chemistry and materials science.
Marco Masia (University of Sassari) - Organiser
Elvira Guardia (Universitat Politècnica de Catalunya, Barcelona, ) - Organiser