# Example 08: Temperature scaling two ways#

Finding the free energy as a function of the temperature can be calculated using reversible scaling methodology (mode ts) as discussed in previous examples.

However, calphy provides another mode tscale that can be used for the same purpose. In this example, ts and tscale modes are compared. Before that:

• What is the difference between ts and tscale?
ts performs reversible scaling method. Here, the simulation is performed at a constant temperature; but the potential energy is scaled. In tscale, the temperature is directly scaled.
• Why do we need tscale?
If ts mode works for the given potential, it should be used. ts, however, needs the pair hybrid/scaled <https://docs.lammps.org/pair_hybrid.html>__. If this is not possible due to some restriction of the potential, tscale can be used.

The input file is given in input.yaml. There are two sets of calculations, one with mode tscale, and another one with mode ts that can be used for comparison.

The calculation can be run by,

calphy -i input.yaml


After the caculation is over, we can plot the free energy as a function of temperature.

[1]:

import numpy as np
import matplotlib.pyplot as plt

[2]:

t1, fe1, ferr1 = np.loadtxt("ts-FCC-1200-0/temperature_sweep.dat", unpack=True)
t2, fe2, ferr2 = np.loadtxt("tscale-FCC-1200-0/temperature_sweep.dat", unpack=True)

[4]:

plt.plot(t1, fe1, color="#E53935", label="ts")
plt.plot(t2, fe2, color="#0097A7", ls="dashed", label="tscale")
plt.xlabel("Temperature (K)", fontsize=12)
plt.ylabel("F (ev/atom)", fontsize=12)
plt.legend()


As seen from the plot above, both modes agree very well with each other. Now we can compare the error in both methods.