I have constructed mono layer slab of rutile TiO2 (110) with 11 Angstroms vacuum between two layers. I used the Quantum wise software for the construction of the slab. Then I have exported the Quantum espresso input from Quantum wise software. Now the problem is the SCF calculations are not converging upto 500 iterations. Do I need to increase the number of iterations? If that so what is the maximum possible number of iterations ? Or else what is the problem in converging? Friends Your suggestions will be valuable for my calculations. Thank You in advance.