A theoretical study of the Knight shift and its volume dependence for Li, Na, and K

The augmented plane wave method, in the muffin-tin approximation, was used to perform self-consistent spin-polarized calculations of the electron number densities, n(r), and spin magnetic moment densities, m(r), within the framework of the spin density functional formalism. For the exchange-correlation energy functional we used the new improved results of Vosko and coworkers in the local spin density approximation. The calculations were carried out for the range of volumes 0.9 ≤ V/V0 < 1. The contributions to the total Fermi contact term, m(0), relative to the Fermi surface contribution, were approximately −24, −2, and −2% from the core electron polarization and −0.7, −5, and −6% from the polarization of the valence electrons below the Fermi surface, for Li, Na, and K respectively. In Li the volume dependence of m(0) was strongly affected by the volume dependence of the core contribution, which differed markedly from that of the Fermi surface contribution. In both Li and K the calculated volume dependence for small volume changes was in good agreement with recent experiments, while in Na the trend was correct but the slope of the curve was too large. In all cases the results were very sensitive to achieving a high degree of self-consistency. The absolute values of m(0) are in excellent agreement with the measured Knight shifts.