My question is about finite difference modeling of EM fields.

Exist some methods to force numeric divergence be zero,

not changing too much the overall field picture?

Like [E(x+dx,y,z) - E(x-dx,y,z)] / dx + [E(x,y+dy,z) - E(x,y-dy,z)] / dy + [E(x,y,z+dz) - E(x,y,z-dz)] / dz = 0.

Theoretically Maxwell equations maintain divergence stable,

but numeric errors accumulate.Or it maybe necessary setting initial field state.

Thanks in advance.