After proving the good accuracy of the method, we are now exploring the computation time required. We see on Figure that the method reaches an RMSE below 1.0 kJ mol -1 very quickly for an average CPU time of 1.2 s (Table ), corresponding to 2,000 sampling points per atom. This is far less than the 150 s (Table ) required for a Widom insertion to reach its plateau value, for an RMSE of 0.10 kJ mol -1 with 12,000 cycles. Moreover, the Widom insertion needs around 14 s to reach a similar RMSE of 1.0 kJ mol -1 , which is still slower than the surface sampling. We can conclude that this initial implementation of the surface sampling is faster than a standard Widom insertion, with a good accuracy.