/usr/share/gromacs/top/gromos45a3.ff/ is in gromacs-data 2018.1-1.
This file is owned by root:root, with mode 0o755.
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/usr/share/gromacs/top/gromos45a3.ff/aminoacids.c.tdb
/usr/share/gromacs/top/gromos45a3.ff/aminoacids.hdb
/usr/share/gromacs/top/gromos45a3.ff/aminoacids.n.tdb
/usr/share/gromacs/top/gromos45a3.ff/aminoacids.r2b
/usr/share/gromacs/top/gromos45a3.ff/aminoacids.rtp
/usr/share/gromacs/top/gromos45a3.ff/aminoacids.vsd
/usr/share/gromacs/top/gromos45a3.ff/atomtypes.atp
/usr/share/gromacs/top/gromos45a3.ff/ff_dum.itp
/usr/share/gromacs/top/gromos45a3.ff/ffbonded.itp
/usr/share/gromacs/top/gromos45a3.ff/ffnonbonded.itp
/usr/share/gromacs/top/gromos45a3.ff/forcefield.doc
/usr/share/gromacs/top/gromos45a3.ff/forcefield.itp
/usr/share/gromacs/top/gromos45a3.ff/ions.itp
/usr/share/gromacs/top/gromos45a3.ff/spc.itp
/usr/share/gromacs/top/gromos45a3.ff/spce.itp
/usr/share/gromacs/top/gromos45a3.ff/tip3p.itp
/usr/share/gromacs/top/gromos45a3.ff/tip4p.itp
/usr/share/gromacs/top/gromos45a3.ff/watermodels.dat