Exchange Core-Polarization Contribution to the Spin Density in Liquid Metals

A theory is developed for the exchange core-polarization (ECP) contribution to spin density $S^{\mathrm{cp}}$ in liquid metals in the framework of moment-perturbation (MP) procedure and pseudopotentials. The zero-order contribution to $S^{\mathrm{cp}}$ has been shown to be temperature independent while the first-order term depends on the temperature through the liquid-interference function. The results give a definite trend for convergence of the perturbation theory. In the specific case of liquid Mg the ECP contribution to the Knight shift $K_s^{\mathrm{cp}}$ is about 25% of the direct shift $K_s^d$ and varies rather slowly with temperature in comparison to that of $K_s^d$. From the present results it seems that the Fermi-contact term is the most dominant term and determines the major change of the Knight shift with temperature in agreement with what has been predicted previously.