OpenMM does not give progress for minimization, just wait...
tetraloop_mdr.pdb ...
1 nm
Energy at Minima is -14996.692 kcal/mol
saved  tetraloop_mdr_min.pdb
Cmd: rna_minimize.py -sp tetraloop_mdr.pdb
Execution time: 2:36:22.479  start: 21:20:37 end: 23:57:00  
DONE!