The heat capacity of solids is usually computed by the Dulong-Petit rule:
Cv = 3R
This expression gives acceptable values only at high
temperatures. Debay has given a more general
formula based on the vibrational modes of the crystal.
Some values for the Debay temperature are as follows:
In order to plot this function the temperature is defined as an array, for example from 10 to 400 K, with a step of 10 K. Then the heat capacity is computed for each temeprature.