Dear Giovanni, Thank you so much for your explanatory response. So, as I understood, there is no way to calculate band structure for a molecule and this is nonsensical. Is it true?
On Nov 29, 2016 1:46 AM, <meisam....@gmail.com> wrote: > Just to add that plain wave is not a good approximation to reproduce > molecular orbitals. > > Mortaza A > > PhD of Physics > Ulm University, Germany > > On 28 Nov 2016, at 21:43, Giovanni Cantele <giovanni.cant...@spin.cnr.it> > wrote: > > 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 > > > _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum >
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