To tackle the problem of charged polymer brushes, I start by guessing its grand potential functional. This is a fundamental step in constructing a DFT framework. The guess is based on the physical properties of the particles in the system. Here, we have positively charged linear chains that are densely grafted to a neutral surface. These chains are suspended in a solvent which is mostly water. In this condition, due to the fact that water is a polar liquid, the counterions dissociate into the solvent to satisfy the electroneutrality principle.