Problem in convergence in Quantum espresso

[Arun Prasath]

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.

 

[TeethWhitener]

This is a tough question to answer without knowing more. SCF calculations will sometimes fail to converge because you haven’t given them enough iterations; however, 500 should be plenty. Another cause is that the convergence criteria are to tight. The program signals convergence when the change between iterations falls below some threshold parameter that’s usually adjustable. If this parameter is set too low, the program can have trouble reaching convergence within the number of iterations.

There are also more physically motivated problems that can prevent calculations from converging. For example, most ab initio programs require some sort of initial guess for the electronic state. If this guess is totally off-base, the calculation can have trouble converging.