I've read papers in DFT studies on band gap tuning in semiconductors and the usually studied methods are either through doping or application of external strain. But its always just one or the other. I've never come across any paper where they investigated how simultaneously varying both the amount of doping and strain affects the electronic structure of materials. Why is this so? Is there some physics-based reason for this or is it just because simultaneously varying both the amount of doping and strain is computationally expensive?