Dear All

I need to optimize a slab of (2*2) surfaces of TiO2 (111) with 10A vacuum in Z. I used the following steps:

1- Optimization of TiO2 unit cell with cell lengths and ionic positions as variables.

2- Building 2*2*2 supercell from optimized unit cell of step1.

3- Optimizing supercell of step2 with both cell lengths and ionic positions as variables.

4- Cleaving (111) surface from supercell of step3.

5- building slab.

6- Optimizing the slab with only ionic positions as variables.

Is it correct or not?

Can I remove cell optimization in step3 (i.e., only considering ionic positions as variables)?