Comment on: "Phenomenological model of Dynamic Nonlinear Response in   Relaxor Ferroelectrics
  In a recent paper (A.E. Glazounov and A.K. Tagantsev, Phys.Rev. Lett. 85, 2192 (2000)) it has been proposed a phenomenological model of the dynamic non-linear response in relaxor ferroelectrics based on the averaging of the Landau-Khalatnikov equation over the distribution of the relaxation times. The purpose of the present comment is to clarify the physical assumptions involved in the Glazounov-Tagantsev approach and show that models based on the Landau-Khalatnikov equation can not describe properly the dynamic response in relaxor ferroelectrics. 
B.E. Vugmeister and H. Rabitz