if you try to ask the question: "what the k-point mesh is for?" you can easily understand that a k-point mesh is for the Brillouin zone (BZ) sampling, that is, perform sums over k-points that approximate, with a required level of accuracy, the integral over the whole BZ. This is because in a crystal, the energy E(K) depends on the k vectors, and the same holds for the wave functions. However, when you build for example a cubic supercell including vacuum to simulate a molecule, you are actually dealing with a fictitious cubic crystal where the repeated units are sufficiently far apart from each other to not interact.
Absence of interaction means flat (atomic-like) energy levels, that do not have dependence on the k vector. That is, the E(K) dispersion that you get in the case of a molecule, provided you include a sufficient vacuum space in your supercell, does not depend on k. If this is the case, you can use only the gamma point (a larger grid means large but useless computational time, because you are summing over eigenvalues at different k-points that are all the same!) for self consistency and BZ path is not needed, because if you select any path you should get flat, k-independent bands Giovanni > On 28 Nov 2016, at 18:12, ashkan shekaari <sheka...@gmail.com> wrote: > > Dear experts, > > Is it necessary using kpoint mesh when we are dealing with molecules? > > In the case of a molecule in cubic vacuum, what path in BZ should be selected? > -- > Regards, > Ashkan Shekaari > Plasma Physics Research Center > Science and Research Branch > I A U, 14778-93855 Tehran, Iran. > _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum
_______________________________________________ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
