# Warmup exercise and example of post

Reproduce Fig. 2.1 of the book .

For this calculations the authors used a cutoff energy of 292 eV and a $$\vec{k}$$ point mesh of 12x12x12. The exchange and correlation is (Perdew-Wang 91).

Example of an equation

$$f(x)=\sum_{s=-\infty}^{+\infty}e^{-i2\pi xs}g_s\label{fourier}$$

with $$g_s$$ given by

$$g_s=\int_n^{n+1} dx f(x) e^{i2\pi sx} \label{fourier-coefficient}\;.$$

We can evaluate Eq. \eqref{fourier} at the point $$n+\gamma$$ with $$\gamma\in[0,1]$$ to obtain