Hello,

in VASP, adding or removing electrons from the system will result in the code adding a homogeneous background charge to maintain overall charge neutrality. To avoid this, there are a few methods you can try.

One method is to use charged supercells. Instead of adding or removing electrons, you can create a charged supercell with a larger unit cell and extra charge carriers (like dopants, vacancies, or interstitials) to maintain charge neutrality. This allows you to study charged systems without introducing the homogeneous background charge. However, this approach can increase computational costs because of the larger system size.

Another option is to use other DFT software. VASP may not be the most suitable software for studying charged systems without a homogeneous background charge. Other DFT software packages like Quantum ESPRESSO, ABINIT, or CP2K allow for studying charged systems without imposing a background charge. However, each software has its own syntax and methodologies for handling charged systems, so you'll need to consult their respective documentation for specific guidance.

So, VASP adds a homogeneous background charge when you add or remove electrons from the system, but you can use charged supercells or explore other DFT software packages to study charged systems without this artifact. Just remember that each software has its own unique syntax and methods, so make sure to read their documentation for specific guidance.