Theory of Knight Shifts and Relaxation Times in Alkali Metals-Role of Exchange Core Polarization and Exchange-Enhancement Effects

The current situation with respect to theory as compared to experiment for Knight shifts and relaxation times in alkali metals is discussed. The roles of exchange core polarization effect and exchange enhancement of the susceptibility due to electron-electron interaction are discussed in detail. It is shown that through a consideration of these effects, combined with the relativistic corrections to the spin density for heavier alkali metals, one is able to obtain an over-all agreement with experiment. However, quantitative agreement with experiment is still lacking, and several additional contributing mechanisms are briefly discussed. The need for better treatments of exchange-enhancement effects on the susceptibility for Bloch electrons and more accurate wave functions, particularly for the lighter metals lithium, sodium, and potassium, is pointed out.