Hi,
Thank you for your reply.
I have given the parameters in my question. When I asked this question my main concern was If I can go for a higher stress and force settings to improve time.The unit cells in most cases consist of 3 atoms (take MoS2 for example) and can be obtained from materials project. Inside geometry optimization I use 0.01eV/Ang max_force, 0.001 eV/Ang max_stress. Steps 200 and nothing is constrained (neither x,y,z nor bravais lattice). I guessed that the cut-offs above are already rigorous so that shouldn't be a problem. One thing to clarify though that the supercells are very large (8x8x1). As far as I have read in journals, people don't use such large cells (mostly 5x5x1 supercells). I had to use bigger for consistency and because of previous experiences with certain materials. So using 1x1x1 k points for supercells won't be a problem. In case of single unit cells it will cause problems and ATK detects that I should use 4x3x1 k-points in general, but to be safe across all materials I go with 5x5x1 k-points (With 20 Ang vacuum, the z direction is way too big to use more k points. Of course I can use but I shouldn't have to). Other settings in Geometry optmization are standard LBFGS and 0.2 Ang step size.
Thanks