  Local pseudopotential (LPP) is an important component of the orbital free
density functional theory (OF-DFT), which is a promising large scale simulation
method that can still maintain information of electron state in materials. Up
to date, LPP is usually extracted from the solid state DFT calculations. It is
unclear how to assess its transferability while applying to a much different
chemical environment. Here we reveal a fundamental relation between the first
principles norm-conserving PP (NCPP) and the LPP. Using the optimized effective
potential method developed for exchange functional, we demonstrate that the LPP
can be constructed optimally from the NCPP for a large number of elements. Our
theory also reveals that the existence of an LPP is intrinsic to the elements,
irrespective to the parameters used for the construction. Our method provides a
unified method in constructing and assessing LPP in the framework of first
principles pseudopotentials.
