Acquisition functions. An important contributor to hit discovery is the so-called acquisition function. The acquisition function determines which molecules are selected for screening and how the training set is expanded, governing hit retrieval and influencing future iterations. Six acquisition functions were investigated as a strategy to select molecules for the next cycle, and for their effect on the active learning performance: , molecules with the lowest mutual information (Eq. 8) are selected from the screening library. Mutual information is low when there are many possible ways of predicting the data with high certainty, given the same model.