Theoretical approaches to charged surfaces

Abstract

We summarize some of our recent theoretical and numerical work on the behaviour andstructure of charged surfaces. Due to the coupling of effects on vastly different lengthscales, a complete treatment of charged surfaces is out of reach with present computerpower. On the other hand, some progress can and has been made by concentrating on onespecific aspect at a time with a suitably chosen numerical method. We discuss four suchcalculations, each using a different computational scheme, that yield various levels ofdescription of charged surfaces. (i) Coarse grained Monte Carlo simulations of idealizedsurfaces incorporate large-length-scale fluctuation and correlation effects in thecounterion cloud at a charged surface. (ii) Brownian dynamics simulations ofmore realistic, structured surfaces give modified counterion distributions andalso allow one to estimate dynamic and non-equilibrium quantities such as themobility of counterions at charged surfaces. (iii) All-atomistic molecular dynamicssimulations of water at surfaces correctly reproduce water structuring effects atsurfaces such as hydration and hydrophobic dewetting. (iv) On the nanoscopic level,quantum mechanical ab initio calculations give the effective interactions betweenoppositely charged groups in vacuum and in solution. The real theoretical challenge isto correctly piece together results obtained on all these different length scales.