PAT (Profit after Tax) arrives after deducting Tax from PBT, which should be discounted by Ko (Cost of Capital). Because Ko is arrive by weighted average of Ke & Kd (i.e. We *Ke + Wd * Kd)
Where Kd = Debt Interest rate (1-tax) i.e. interest rate net of tax
Ke = cost of equity
We = weight of equity
Wd = weight of debt