What is smearing?

Usually, during the calculation of density of states, smearing is used. There are different types of smearing applied. Each may have its advantages/disadvantages. Some times there may be no apparent physical meaning.

Following is from SE site. 

"The smearing in density functional theory codes means that you occupy the states of the Kohn-Sham system according to a smooth function, e.g., the Fermi distribution. It is introduced to avoid numerical problems partly due to the finite sampling of the Brillouin zone and partly due to properties of the investigated system.

One example: Consider a metal with rather flat bands at the Fermi energy. If you have no temperature smearing than such a band may be completely occupied if it is slightly below the Fermi energy or completely unoccupied if it is slightly above the Fermi energy. Now consider your self-consistency cycle. In this cycle the band can shift in energy from iteration to iteration. It can be occupied in one iteration and unoccupied in the next. This means that the charge density can change strongly from one iteration to the next and such an effect may impede the convergence to a self-consistent solution. If you introduce a temperature smearing for the electronic system you obtain smoother changes of the occupations. The mixing algorithms that produce the next charge density from the charge densities of the previous iterations can deal better with such a situation.

That being said density functional theory is a ground-state theory. That means it is made for no temperature smearing of the electronic system. The self-consistent ground-state charge density that you want to obtain is the charge density for 0K. Thus the temperature smearing has to be seen as a convergence parameter. You may set it to a high temperature of 1000K or so to overcome larger convergence problems and then you go on and reduce it until your results don't change any more." 

For more details, see following pages.

Gregor Michalicek (https://physics.stackexchange.com/users/166799/gregor-michalicek), What do we physically mean by smearing in condensed matter?, URL (version: 2017-09-29): https://physics.stackexchange.com/q/360044