i.e. 1/ k 0 is given by the familiar formula for Debye length. In the opposite extreme, in the low-temperature limit T = 0, electrons behave as quantum particles (fermions). Such an approximation is valid for metals at room temperature, and the Thomas–Fermi screening wavevector k TF given in atomic units is k T F 2 = 4 ( 3 n π π ) 1 / 3 .