OpenMM does not give progress for minimization, just wait...
tetraloop_mdr.pdb ...
1 nm
Energy at Minima is -14930.988 kcal/mol
saved  tetraloop_mdr_min.pdb
Cmd: rna_minimize.py -sp tetraloop_mdr.pdb
Execution time: 0:05:23.362  start: 23:40:18 end: 23:45:42  
DONE!