You are referred to band theory of solids and then analyze your results. For semiconductors, there should be energy gap across the Fermi level, however, in case of metallic system the valence and conduction bands overlap across the Fermi level.

within band theory if the density of state at the fermi energy is non zero you have a metal.

To be sure you may have to test robustness of the results w.r.t. number of k-points and smearing width but this is the basic idea.

thanks both of you for your valueable answer

Dear Amrish:

You can take a look to my web page:

http://personales.unican.es/junqueraj

and follow the links 

A self explained SIESTA Tutorial

Set of self-explained SIESTA Exercises

Computing structural and electronic properties of materials

and

Converging the simulations

You will find there many examples, all of them fully explained, about how to compute and analyze the band structures and density of states of metals and insulators.

Hope this helps,

Javier