Fig. 1. Overview of stk-search. Summary of the procedures implemented in stk-search to explore the chemical space of molecules constructed from building blocks. Starting from a fragment database, we first define the chemical space by generating building blocks with specific connection points, and then establish the size and the connection rules to build the molecules (1). Next, we define an evaluation function where we build the molecules and evaluate their properties using quantum chemistry methods (2). Finally, using an appropriate search algorithm, we can explore the chemical space (4–5) and find molecules with the desired property.