I am trying to simulate a protein with a peptide in GROMACS using CHARMM36 force field and TIP3 recommended water model. After the EM step I see that the potential energy is positive and the curve shows a steep decline and not the usual exponential decline. I then tried reducing the maximum force by changing emtol to 100 from 1000kJ/mol/nm and yet obtain the same curve. Does anyone know what went wrong?

I am attaching a picture of the curve plotted using Xmgrace. I have changed the X-axis co-ordinate of the curve to 10 pico-second to visualize the curve.