Chimera PDB fetch is broken starting November 3 and a command like "open 1a0m" produces an empty model with no error. We will be putting a new version (release candidate) of Chimera on the download page today or tomorrow that fixes this. What happened is that the RCSB has shutdown the URL Chimera uses to fetch PDB files (e.g. https://www.rcsb.org/pdb/files/1a0m.pdb <https://www.rcsb.org/pdb/files/1a0m.pdb>). Although RCSB announced this long ago the Chimera development team missed that this URL was going away. Tom