Abstract
Dense quantum plasmas are of high current interest in astrophysics and many laboratory experiments. Quantum hydrodynamics (QHD) became a popular model because it is much simpler than ab initio approaches such as quantum kinetic theory, nonequilibrium Green functions methods, time-dependent density functional theory and quantum Monte Carlo2.Particularly, nonlinear waves are easily accessible using QHD. However, often QHD is used outside the range of applicability and even with incorrect explicit expressions as discussed in Refs.3–5.