Wave-Number-Dependent Susceptibility Function for Paramagnetic Chromium

A detailed computation has been made of the generalized susceptibility function for paramagnetic chromium to investigate the effects of including realistic band-structure effects on both the unenhanced susceptibility and on the exchange enhancement. An augmented-plane-wave band-structure calculation for paramagnetic chromium has been performed to obtain energy bands and wave functions for the first six bands on a mesh of 1024 points in the Brillouin zone. An interpolation scheme was used to increase the effective mesh to 128 000 points in the zone and the unenhanced susceptibility function was calculated from these, both with and without the matrix elements. The matrix elements were seen to make a dramatic difference in the susceptibility, and, in fact, reduce the peak due to the "nesting" of the Fermi surface so that it is not an actual maximum of ${\lambda }^{\mathrm{}\left(0\right)\mathrm{}}\left(\overrightarrow{\mathrm{q}}\right)$. The exchange enhancement was then investigated by approximately solving the coupled self-consistent equations for the Fourier components of the response to an applied field including local-field corrections. This yields an exchange-enhanced susceptibility function which has the tendency to first become infinite at the nesting wave vector, indicating that the local-field corrections may play an important role in determining the wave vector for instability against formation of a spin-density wave. It is also shown that the exchange-enhanced susceptibility thus obtained displays quasilocalized spin behavior of the electron response to an applied oscillatory field.