Dear Roshan,

The length unit in Gromacs is 'nm' and there is no way to change the defaults (if you can find the related code in the Gromacs package you can change it though). However, with a simple sed, awk, programming or even gnuplot you can reach your goal of converting units to angstrom.

Good luck!

1 nm = 10 Angstrom. Simply multiply the Gromacs output by 10.

I don't understand the question. But if you are asking on how to show that units on the axis label in Angstroms in xmgrace, then you should write the label as follows:

RMSD(\cE\C)

If you are trying to convert the units inside xmgrace, you should use:

Data > Transformations > Evaluate Expression> y = y *10