This example considers the Cohen-Bergstresser model[CB1966], reproducing the results of the original paper. This model is particularly simple since its linear nature allows one to get away without any self-consistent field calculation.
We build the lattice using the tabulated lattice constant from the original paper, stored in DFTK:
using DFTK Si = ElementCohenBergstresser(:Si) lattice = Si.lattice_constant / 2 .* [[0 1 1.]; [1 0 1.]; [1 1 0.]] atoms = [Si => [ones(3)/8, -ones(3)/8]];
Next we build the rather simple model and discretise it with moderate
Ecut = 10.0 model = Model(lattice; atoms=atoms, terms=[Kinetic(), AtomicLocal()]) basis = PlaneWaveBasis(model, Ecut, kgrid=(1, 1, 1));
We diagonalise at the Gamma point to find a Fermi level ...
ham = Hamiltonian(basis) eigres = diagonalize_all_kblocks(DFTK.lobpcg_hyper, ham, 6) εF = find_fermi_level(basis, eigres.λ)
... and compute and plot 8 bands:
using Plots n_bands = 8 ρ0 = guess_density(basis) # Just dummy, has no meaning in this model p = plot_bandstructure(basis, ρ0, n_bands, εF=εF, kline_density=10) ylims!(p, (-5, 6))