Figure depicts the host-guest binding free energies extracted from the GCNCMC titrations, compared to experimental data and a basic ABFE approach which uses a flat bottom restraint to keep the guest bound as it is decoupled. In general, a slight overestimation of the binding affinities relative to experiment was observed, prompting speculation that the forcefield parameters used may not be optimal, with similar trends having been reported previously. Despite this, the calculations gave a mean absolute error (MAE) and root mean squared error (RMSE) with respect to experiment of 0.7 and 0.6 kcal mol -1 with almost all the data points falling within 1 kcal mol -1 of the experimental value. Furthermore, the correlation (R 2 = 0.94) and ranking (τ = 0.84) with respect to experiment shows that the method can reliably and accurately rank fragments in terms of their binding affinities. An almost perfect correlation with the more well-established FEP approach gives promising validation. Fig. : Calculated binding free energies from titration calculations vs. experiment and FEP results, using a flat bottom restraint.