Molecular Descriptor Computational Methods Available in SMARTpy. In UCSF Chimera, the command molmap was used to enclose the probe conformers in a molecular surface from which VCAVITY and ACAVITY were computed (Figure ). The molmap function in UCSF Chimera is a density-based computation that computes a surface around select atoms in a manner proportional to the atomic numbers. Open-source Python packages were implemented instead for either speed or expanded functionality to compute SMART descriptors from probe ensembles.