New empirical form factor for the alkali metals sodium and potassium

A method is presented for obtaining a highly accurate empirical form factor v(q) for the alkali metals from the measured temperature dependence of the electrical resistivity. Two parameters are required for v(q), one determined from the high-temperature and the other from the low-temperature resistivity data. The method is applied to potassium and sodium. The error in the resulting v(q) does not exceed 0.002 Ryd for potassium and 0.003 Ryd for sodium throughout the range q<or=2k_F.