  We study the self diffusion of individual particles in dense (non-)uniform
complex fluids within dynamic density functional theory and explicitly account
for their coupling to the temporally fluctuating background particles. Applying
the formalism to rod-like particles in uniaxial nematic and smectic liquid
crystals, we find correlated diffusion in different directions: The temporary
cage formed by the neighboring particles competes with permanent barriers in
periodic inhomogeneous systems such as the lamellar smectic state and delays
self diffusion of particles even in uniform systems. We compare our theory with
recent experimental data on the self diffusion of fluorescently labelled
filamentous virus particles in aqueous dispersions in the smectic phase and
find qualitative agreement. This demonstrates the importance of explicitly
dealing with the time-dependent self-consistent molecular field that every
particle experiences.
