Specific heat per spin (FIG 8.10)

The specific heat per spin is calculated according to the fluctuation-dissipation theorem:

Equation 1. fluctuation-dissipation theorem

Where T is the temperature at a given point, Kb is the Boltzmann’s constant and (ΔE)^2 is the total energy variance and can be calculated as follows: 

Equation 2. total energy variance

Where < E >^2 is the average energy level and < E^2 > is the average squared energy level:

Figure 1. Specific heat simulated

Figure 2. Specific heat computational physics by Giordano (Fig 8.10) [1]