Nonlocal Pseudopotential and the Fermi Surfaces of the Alkali Metals

Abstract

The nonlocal pseudopotentials in the OPW formalism are determined for sodium and potassium from the experimental data in the radial distortion of the Fermi surfaces, by taking the core shift in the pseudopotential as an only adjustable parameter to fit the data. It is found that the exchange interaction between core and conduction electrons should be treated properly without using the approximate form like the slater exchange to find a reasonable value for the core shift parameter. The exchange and correlation effects among conduction electrons are taken into account in the approximate form proposed recently by Kleinman and are found to be also important. The nonlocality of the determined pseudopotentials is quite significant; the validity of the local pseudopotential approximation seems rather limited. The reason why the analysis of the Fermi surface distortion by using the local pseudopotential has been quite successful for Na but not for K is discussed.