4.20. Smeared occupations¶

This example calculates an aluminum crystal with smeared occupations. It explains how the calculation and the energies are interpreted.

from eminus import Cell, RSCF
from eminus.tools import get_Efermi
from eminus.units import ha2kelvin

Create a cell for an aluminum crystal

Set a smearing value in atomic units

The resulting SCF will use a Fermi-Dirac function to smear the occupations over the selected bands

cell = Cell("Al", "fcc", ecut=10, a=7.63075, bands=6, smearing=0.01)

Create the SCF object

The occupations update per SCF cycle can be controlled with the smear_update parameter

scf = RSCF(cell, etol=1e-5, verbose=0)
scf.smear_update = 1

Do the DFT calculation

scf.run()

The resulting total energy includes an entropic term when smearing is enabled

print(scf.energies)

We can extrapolate the energy to T=0

print(f"\nEtot({ha2kelvin(cell.occ.smearing):.2f} K) = {scf.energies.Etot:.6f} Eh")
print(f"Etot({0:>7.2f} K) = {scf.energies.extrapolate():.6f} Eh")

Calculate the Fermi energy

print(f"\nEf = {get_Efermi(scf):.6f} Eh")