function init_pot_Hcoul( LF, center )
  Npoints = LF.Nx * LF.Ny * LF.Nz
  Vpot = zeros( Float64,Npoints )
  for ip = 1:Npoints
    r = norm( LF.lingrid[:,ip] - center[:] )
    Vpot[ip] = -1.0/r
  end
  return Vpot
end
