Scf did not converge. Can anyone help me?

I am tring to Geometry Optimize Cobalt nanocluster using Dmol3/ GGA. At last i come up with the message which is stated below. Well i get the convergence when i change the smearing value to 0.7, but this value is very high i guess.

Error: SCF iterations not converged in 1000 iterations

DELTE =   1.000000000000000E-008

Message: SCF not converging. Choose "Use Smearing" on DMol3 SCF panel

or set "Occupation  Thermal" in the input file.

You may also need to change spin or use symmetry.

Resubmit DMol3.

Message: DMol3 job failed

Error: DMol3 exiting