STgrow4 fitness function value = Vina_score -W * STLogBB STLogBB was the same as the LogBB calculated from the PLS-Regression models described above for predicted values less than a maximum of 1.7 and more than a minimum of -2.15. Values of LogBB predicted to be higher or lower than these bounds were truncated to the upper limit or lower limit of the range, respectively. W is a parameter that can be tuned for each application. The effect of W on the distribution of designed molecules was investigated using values of 1.0, 1.5 and 2.0. All other parameters were the same as those used for Autogrow4.