[gmx-users] If the system net charge is zero, do I need to add ions?

["Dr. Ramón Garduño-Juárez"]

Hi GROMACS users,

I've two questions. My simulation box contains a DMPC lipid bilayer, 
water molecules, intramembrane protein and a ligand protein. The net 
charge of the system is zero. Is it necessary to add ions to this system?

The intramembrane protein (made of two chains) has a net charge of -1 
and the ligand protein has a net charge of +1, thus the net charge of zero.

The next question is too naive, but if the ions are needed, What ion is 
better for the dynamics K or Na?

Much obliged.
Eduardo.
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