# what do I need to change about typical VASP input file to calculate the energy of a single atom?

I'm a little confused how to make a VASP input file to calculate the energy for the isolated atom:

1. Do I need to change the lattice parameter of my unit cell or can keep the value for the whole system?

2. If I have 4 atoms of one type in my unit cell, can I consider the position of any of them or must it be in the middle of the unit cell?

3. I observed that some people use K point set $$1\times1\times1$$ for calculating a single atom. Is it necessary to use this set or can I use the normal K points set that is used at the time of convergence?

To boil it down to one question, what do I need to change about typical VASP input file to calculate the energy of a single atom?

Isolated atom itself mean that there is no interaction from other nuclei , Hence box needs to be large enough so that atom doesn't interact with periodic image. In general 10-15 Angstrom size of box is enough. Once box is defined large (cubic) enough, placing atom anywhere inside box will not result any interaction from periodic image. If real space is large enough, reciprocal image will shrink to a point and number of kpoints will boil down to single point, Hence 1x1x1 is used for energy calculations. Better to look at OUTCAR to check reciprocal space lattice parameter and volume