Box and atom coordinate scaling not consistent when converting from GROMACS to LAMMPS

[chw90]

Environment Information

Open Babel version: 3.1.1
Operating system and version: Ubuntu 22.04

Expected Behavior

The coordinates of atoms and the coordinates of the simulation box bounds are either unchanged or at least scaled with the same factor.

Actual Behavior

Atom coordinates are scaled with a factor of 10. Box bounds in the LAMMPS data file seem uncorrelated with the box vectors given in the GROMACS data file.

Steps to Reproduce

• An example GROMACS input file is attached (file extension renamed to .txt so GitHub accepts it).

$ mv ice1htip3p.txt ice1htip3p.gro
$ obabel ice1htip3p.gro -olmpdat > ice1htip3p.lmpdat

Now compare the GROMACS box vectors (last line of the `.gro file) and the LAMMPS box sizes:

$ tail -n 1 ice1htip3p.gro
    2.34685163 2.20607179 2.71095555
$ cat ice1htip3p.lmpdat | grep -e ".lo" -e ".hi"
  -0.59000   27.21000 xlo xhi
  -0.59000   27.21000 ylo yhi
  -0.59000   27.21000 zlo zhi

Expected result would be:

$ cat ice1htip3p.lmpdat | grep -e ".lo" -e ".hi"
   0.00000   23.4685163 xlo xhi
   0.00000   22.0607179 ylo yhi
   0.00000   27.1095555 zlo zhi

Is this expected behavior? Does Open Babel compute the simulation box itself based on the atoms instead of taking the definition of the GROMACS input?

ice1htip3p.txt

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