Problem in running lammps when system is not charge neutral

Dear all,
I want to simulate the process of heterogeneous nucleation (containing ions (40 na+)) of supersaturated water vapor, and PPPM is used to compute the long-range coulombic interactions. 
Thus, net charge of my simulation system is not zero, there is a warning in lammps: system is not charge neutral, net charge=40. 
I do not know whether the result is available if I ignore the warning? What should I do? Does lammps can accurately simulate the system which is not charge neutral?
I will appreciate if you can give me some suggestions!

Best regards
Zhang Chao