Abstract & Overview
This thesis work is devoted to the conceptual and technical development of\nthe Adaptive Resolution Scheme (AdResS), a molecular dynamics method that\nallows the simulation of a system with different levels of resolution simultaneously.\nThe simulation domain is divided into high and low resolution zones and\na transition region that links them, through which molecules can freely diffuse.\nThe first issue of this work regards the thermodynamic consistency of the\nmethod, which is tested and verified in a modelliquid of tetrahedral molecules.\nThe results allow the introduction of the concept of the Thermodynamic Force,\nan external field able to correct spurious density fluctuations present in the\ntransition region in usual AdResS simulations. The AdResS is also applied to\na system where two different representations with the same degree of resolution\nare confronted. This simple test extends the method from an Adaptive\nResolution Scheme toan Adaptive Representation Scheme, providing a way of\ncoupling different force fields based on thermodynamic consistency arguments.\nThe Thermodynamic Force is successfully applied to the example described in\nthis wor k as well.\nAn alternative approach of deducing the Thermodynamic Force from pressure\nconsistency considerations allows the interpretation of AdResS as a first\nstep towards a molecular dynamics simulation in the Grand Canonical ensemble.\nAdditionally, such a definition leads to a practical way of determining the\nThermodynamic Force, tested in the well studied tetrahedralliquid. The effects\nof AdResS and this correction on the atomistic domain are analyzed by inspecting\nthe local distribution of velocities, radial distribution functions, pressure\nand particle number fluctuation. Their comparison with analogous results coming\nfrom purely atomistic simulations shows good agreement, which is greatly\nimproved under the effect of the external field.\nA further step in the development of AdResS, necessary for several applications\nin biophysics and material science, consists of its application to multicomponent\nsystems. To this aim, the high-resolution representation of a model\nbinary mixture is confronted with its coarse-grained representation systematically\nparametrized. The Thermodynamic Force, whose development requires a\nmore delicate treatment, also gives satisfactory results.\nFinally, AdResS is tested in systems including two-body bonded forces,\nthrough the simulation of a model polymer allowed to adaptively change its\nrepresentation. It is shown that the distribution functions that characterize the\npolymer structure are in practice not affected by the change of resolution.\nThe technical details of the implementation of AdResS in the ESPResSo\npackage conclude this thesis work.