Whereas the first Hohenberg-Kohn theorem states that the total energy of a many-electron system is a unique functional of its electron density, the second theorem indicates that the respective functional returns the lowest energy of the system only if the input density is that system’s ground state density. Considering this, I would rather say that the second theorem is actually complementary to the first one in that both theorems need to be used in tandem to determine of the properties of novel materials via ab inito computational modeling.