[QE-users] Switching to a larger unit cell of the "same" system

[Léon Luntadila Lufungula]

Dear all,

I have been performing calculations on surface-modified TiO2 for the last year by grafting the surface with molecules and comparing the resulting structures and their corresponding energies. In the coming months, I want to expand my work by grafting molecules with longer chains and possibly reducing the modification degree of the surface. In doing so, I would have to increase the size of my unit cell in both the z-direction (to reduce interactions between slabs) and the xy-plane (to allow for a lower modification degree, as the structures I calculated in the smaller unit cell are already at their limit as they contain only one molecule). I understand that I would have to redo convergence tests on both the k-point grid and the energy cutoff (ecutrho) for my larger unit cell. However, I was wondering if there is a meaningful way to compare the structures/energies obtained from the larger unit cell with those of the smaller unit cell, considering that the k-point grid and the cutoff energy might be different? Possibly by matching the cutoff energy and the relative distribution of the k-point grid perhaps? Or would switching to a larger unit cell always require me to recalculate all previous structures obtained in the smaller unit cell?

Thank you in advance.

Kind regards,
Léon Luntadila Lufungula
Master student
University of Antwerp

P.S. This is my first time using the mailing list so feel free to point out any of the posting etiquette I may have disregarded, so I can improve this in the future.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20220812/b7870395/attachment.html>