 Often in a metal the Fermi surface radius formula_17 is larger than the size of the first Brillouin zone which results in a portion of the Fermi surface lying in the second (or higher) zones.As with the band structure itself, the Fermi surface can be displayed in an extended-zone scheme where formula_22 is allowed to have arbitrarily large values or a reduced-zone scheme where wavevectors are shown modulo formula_23 (in the 1-dimensional case) where a is the lattice constant.In the three-dimensional case the reduced zone scheme means that from any wavevector formula_22 there is an appropriate number of reciprocal lattice vectors formula_25 subtracted that the new formula_22 now is closer to the origin in formula_22-space than to any formula_25.