Amino acid positions to diversify
Select several positions (2 to 15) in the active site. The selected positions should not include key catalytic residues performing the chemistry of the catalysis; rather, residues composing the first and second shell of the active site, or in a (in)direct contact with the substrate, should be selected.
The Protein Contacs Atlas can be used to find first and second shell resides.

See Figures 1B and 4A in the FuncLib paper for examples of positions selection.
Important: make sure the chains the library positions are located on are specified in Chain identifier to design