Third year CMP compulsory experiment/The effect of system size
This is the sixth section of the third year CMP experiment. You can return to the previous page, The effect of temperature, or jump ahead to the next section, Determining the heat capacity.
Scaling the System Size
Your plots from the previous section showed how the magnetisation and energy vary with temperature, and you should be able to see the onset of the phase transition. In this region, the energetic and entropic driving forces are of almost equal importance, and large fluctuations in the state of the system can take place. In fact, it is a characteristic of phase transitions that fluctuations within a system start to take place over very long ranges. This is a big problem in our simulation — so far, we only have 64 spins (or "atoms", if you prefer), so our system may not be big enough for these long ranged fluctuations to be correctly modelled.
TASK: Repeat the final task of the previous section for the following lattice sizes: 2x2, 4x4, 8x8, 16x16, 32x32, 128x128. Make sure that you name each datafile that your produce after the corresponding lattice size! Write a Python script to make a plot showing the energy per spin versus temperature for each of your lattice sizes. Repeat this for the absolute magnetisation (why the absolute magnetisation?). As before, use the plot controls to save your a PNG image of your plot and attach this to the report. How big a lattice do you think is big enough to capture the long range fluctuations?
This is the sixth section of the third year CMP experiment. You can return to the previous page, The effect of temperature, or jump ahead to the next section, Determining the heat capacity.
