Anomalous behavior of dispersion curves in water-like systems and water

In the present paper we consider dispersion curves of longitudinal excitations of a model core-softened liquid and SPC/E model of water. We show that both systems demonstrate anomalous behavior of the excitation frequencies: the frequencies of the excitations can decrease with temperature along isochors, while in normal liquids they should increase. This observation allows to introduce one more water anomaly - anomalous dependence of excitation frequencies on temperature.