for example by nijmeijer et al 25 where j ij is the component of the stress tensor and l i is the length of the system in the corresponding direction after the role of each components in the system is clarified two following stages of coarser graining procedure can be applied for these investigation at coarser levels a selection is made step 216 out of many potentially effective additives and or their mixtures and passed on as input to the coarser levels l 2 and l 3 the selection criteria can be based in the simplest case on the highest efficiency of reducing or increasing the ift but is more likely to involve a set of criteria including costs environmental and other operational considerations an example of steps performed at the coarser levels l 2 and l 3 are shown in fig2 b at the stage l 2 components of the model are scaled up to the united atom model step 221 this upscaling operation replaces the atomistic description of the interaction of the molecules with effective potentials describing the interactions of a group of atoms if not introduced in the previous l 1 stage as atomistic model it is at this stage that a molecular description of the rock surface is introduced to ensure consistency between the atomistic calculation at the l 1 stage and this stage l 2 the ift between the oil and water interface is recalculated step 222 the potentials which are introduced when moving from the atomistic model to the united atom model are adjusted until the ift is equal for both levels once consistency is achieved an estimate.