Savrasov S.Y.
A detailed description of a method for calculating static linear-response
functions in the problem of lattice dynamics is presented. The method is
based on density-functional theory and it uses linear muffin-tin orbitals
as a basis for representing first-order corrections to the one-electron
wave functions. This makes it possible to greatly facilitate the treatment
of the materials with localized orbitals. We derive variationally accurate
expressions for the dynamical matrix. We also show that large incomplete-basis-set
corrections to the first-order changes in the wave functions exist and
can be explicitly calculated. Some useful hints on the k-space integration
for metals and the self-consistency problem at long wavelengths are also
given. As a test application we calculate bulk phonon dispersions in Si
and find good agreement between our results and experiments. As another
application, we calculate lattice dynamics of the transition-metal carbide
NbC. The theory reproduces the major anomalies found experimentally in
its phonon dispersions. The theory also predicts an anomalous behavior
of the lowest transverse acoustic mode along the ( xi xi 0) direction.
Most of the calculated frequencies agree within a few percent with those
measured.
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