I made a 3nm×3nm×3nm supercell mesh of pbs atoms which contains about 2000 atoms and QE gave me a 13256 GB requirement of RAM. What am I doing wrong? Many people have already done this calculation, but surely no one has 13TB of RAM available on a single node for a calculation like this.
Memory use to store the KS orbitals in a plane wave DFT calculation is proportional to cell-volume*number-of-states, and in turn proportional to the square of the number of atoms in the large limit. So 13 TB does not surprise me at all. I once computed 4096 Si atoms using CASTEP but that was on a supercomputer, and might easily have used a few TB of RAM.
I respectfully suggest that your claim that "many people have done this calculation" is in error, and that the calculations you may have seen either did not use plane-wave DFT, and/or used a massively parallel supercomputer.
If you still wish to use full KS-DFT for this system, one of the O(N) or linear-scaling local basis set codes would be a more reasonable choice.