We study the dynamics of a spin-\frac{1}{2}12
XXZ chain which is initially prepared in a domain-wall state. We compare
the results of time-dependent Density Matrix Renormalization Group
simulations with those of an effective description in terms of a
classical anisotropic Landau-Lifshitz (LL) equation. Numerous quantities
are analyzed: magnetization (xx,
yy
and zz
components), energy density, energy current, but also some spin-spin
correlation functions or entanglement entropy in the quantum chain.
Without any adjustable parameter a quantitative agreement is observed
between the quantum and the LL problems in the long time limit, when the
models are close to the isotropic point. This is explained as a
consequence of energy conservation. At the isotropic point the mapping
between the LL equation and the nonlinear Schrödinger equation is used
to construct a variational solution capturing several aspects of the
problem.