Double precision normally gives you higher accuracy, but this is often not
needed for preparing to run molecular dynamics.
You might need to increase your constraint accuracy, or turn
off constraints altogether (set constraints = none in mdp file)
writing lowest energy coordinates.
Back Off! I just backed up em.gro to ./#em.gro.1#
Steepest Descents converged to machine precision in 107 steps,
but did not reach the requested Fmax < 1000.