OpenMM does not give progress for minimization, just wait...
tetraloop_mdr.pdb ...
1 nm
Energy at Minima is -15187.722 kcal/mol
saved  tetraloop_mdr_min.pdb
Cmd: rna_minimize.py -sp tetraloop_mdr.pdb
Execution time: 0:05:40.549  start: 11:47:26 end: 11:53:07  
DONE!