Because of VASP license restrictions, we cannot distribute the pseudopotential files (POTCAR) as part of the Materials Project file output. Instead, we have provided a POTCAR.spec file, which specifies the POTCARs used in the Materials Project. To generate an actual POTCAR file, you may either manually do it using the files provided as part of your VASP license, or you can use the gen_potcar.py script in the scripts directory of the pymatgen package (http://pypi.python.org/pypi/pymatgen) that powers the Materials Project. Please note that even if you use the pymatgen package, you will still need to do the necessary configuration setups to point to your pseudopotential files.