Dear Niraja Moharana ,

I think the problem is with smearing, try change the ISMEAR to 0 or -1. In metalic systems occupations of the near valence band edge states are partial and you need smearing such as Fermi-Dirac or Gaussian smearing for convergence of the SCF calculations. Take a loot at these links:

https://www.vasp.at/wiki/index.php/ISMEAR

https://www.researchgate.net/post/How_to_get_corect_band_structure_states_from_DFT_U_and_GW

https://www.researchgate.net/post/How_do_you_choose_ISMEAR_for_a_system_with_metals_insulators_and_semiconductors_in_VASP

Dear Mohammad Shakiba

Thank you for your reply. But by changing the ISMEAR value, I am getting the same error.

Hello,

I'm not sure why it will not do the calculation for a metallic system. You might try changing the choice of ALGO; perhaps EXACT doesn't work for metals.

Also, it's a good idea to increase the number of bands. According to the vasp wiki, "The method selected using LOPTICS=.TRUE. requires an appreciable number of empty conduction band states. Reasonable results are usually only obtained, if the parameter NBANDS is roughly doubled or tripled in the INCAR file with respect to the VASP default. " https://www.vasp.at/wiki/index.php/LOPTICS

Finally, as Mohammad's second link references, a basic VASP calculation will greatly underestimate the band gap of TiN. The experimental band gap is greater than 3 eV, and I recommend you use the DFT + U method to ensure that your calculation is somewhere close to this value. This will have the added benefit of avoiding the "must be insulating" error.Article Electrical and Optical Properties of TiN Thin Films