# What is the maximum allowed doping concentration?

Let's consider an example of a 3x3x1 supercell of WS2 monolayer which has 9 W atoms. If we substitute two of them with 2 dopants, the concentration will be 2/9 which equals approximately 22%. Will this still be called doping? Is it OK to go for it?. If no, what is the maximum concentration allowed for doping?

It really depends on what you want to study. The doping concentration can be changed from 0 to $$100\%$$. Taking the primitive monolayer of MoS$$_2$$ as an example, if you substitute the S atom with Se, then you obtain the MoSSe alloy (alloy engineering method in the field of 2D materials), which can be viewed as $$50\%$$ doping concentration. Furthermore, if you substitute Mo with W then you actually realize the $$100\%$$ doping concentration. But that makes no sense, you just calculate WS$$_2$$ monolayer. For other doping concentrations, you may need to build a supercell. Importantly, how to build the supercell is dependent on what you want to study.