upon recent studies of the Density of states and Specific heat capacities, ive found the Einstien and Debye Models to be very helpful, Debye being the more accurate of the two models at low temperatures as it takes into account the low frequency modes. However, the realistic density of states e.g for solid Argon, seems to not fit either the Debye or the Einstien model at moderate temperatures. The realistic density of states seems to increase faster than any other model as the temperature increases. Why is this? Are there additional modes we are not taking into account?