Gmx make_ndx cannot detect "chain" in GROMACS 2020

GROMACS version:2020 and 5.1.2
GROMACS modification: No
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Dear all,

After trying to make an index file through .tpr, I found that the older version gromacs 5.1.2 can detect chains in the .tpr, while the gromacs 2020 cannot detect chain through the same command. I just wonder is this a bug?

The command that I put for both version:

gmx_mpi make_ndx -f topol.tpr



gmx make_ndx allows to split a group in chain (with the splitch), as soon the chains are properly defined in the topology file.
Sorry, I do not recall what 5.1.2 was doing, you can have a look at the release notes if you want to know what is change and when Release notes — GROMACS 2020.5 documentation

Best regards


I have read the release notes and I didn’t find anything regarding the gmx make_ndx update since 2016. Hence I have no idea what happened.