带正电的体系能量最小化失败

milk_q

体系中有多个NH3+，但没有负电，整体带40+电荷，能量最小化提示：
WARNING 1 [file PPP6-Dex2.top, line 14]:
  You are using Ewald electrostatics in a system with net charge. This can
  lead to severe artifacts, such as ions moving into regions with low
  dielectric, due to the uniform background charge. We suggest to
  neutralize your system with counter ions, possibly in combination with a
  physiological salt concentration这是怎么回事

这是我的steep.mdp

sobereva

用PME这种考虑无穷远距离静电相互作用的方法需要体系净电荷为0，显然应该用gmx genion加抗衡离子（或者自己补上体系中本该存在而没考虑的阴离子）使得净电荷为0，这是基本gromacs使用常识