QuantumATK Forum
QuantumATK => General Questions and Answers => Topic started by: atkbee12 on April 6, 2009, 05:18
-
Hello, I'm new to ATK. I'd like to ask something about mesh cutoff and basis set. For graphene simulations, can I use a mesh cutoff of 100 Ry and a SZP basis set to reduce the computer time? Do these low values for mesh cutoff and basis set affect the results severely?
-
I think the best way is to try.
-
I think that Frsy is right - the best way is to choose a relevant graphene reference system and test on that one what is the implications of the different basis set.
100 Ry mesh-cutoff will in almost no case leads to directly wrong results, but before publishing a paper I would test it on 200 Ry.
Regards the basis set, then normally SZP is a good enough choice, however one must always ask oneself, how different is the environment for this element (Carbon/Hydrogen I guess in your case), to the reference environment of the pseudopotential and the atomic state. So therefore if you start calculating on Carbon in complex multi-element cluster of all kind of different weird materials then SZP is not going to make it, however if you are going to calculate on graphene sheets or similar, then i think SZP would be fine, but as Frsy says, try it out.
-
I have earlier tried some carbon nanotube band structure calculations with as low as 70 Ry without seeing any significant degradation in the results. On the other hand, the actual reduction in time and memory compared to 100 or 150 Ry is not extremely large.
I agree that SZP should be fine to save time for carbon, although you may find it interesting to read a recent article by G. Abadir et al. on precisely the topic of the basis set choice in Journal of Computational Electronics (http://dx.doi.org/10.1007/s10825-009-0263-5).