[Pw_forum] generating k point weights
Dear Stefano Baroni: >YOU have written the answer to your question >"If .true. the bands are classified according to the irreducible representations of the small group >of k" (which is the only sensible thing to do) Sorry, I almost forgot the definition of "small group". I refered to text book and found the answer ?? Thank you for your concise reply ?? Hui Wang School of physics, Nankai University, Tianjin, China -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20090811/f9c371a6/attachment.htm
[Pw_forum] generating k point weights
YOU have written the answer to your question "If .true. the bands are classified according to the irreducible representations of the small group of k" (which is the only sensible thing to do) Stefano Baroni - SISSA Trieste --- swift text written and sent on the go On 11/ago/2009, at 04.02, xirainbow wrote: > Dear Stefano Baroni and Gabriele Sclauzero: > > First of all, thank you very much for your detailed explanation :? > I think I fully undertand it. > First, the "kpoints.x" reduces the number of k-points according to > parameter "ibrav". That means kpoints.x chooses the symmetry among > 14 Bravais lattices. > Second, the "pw.x" checkes all symmetry operations within a given > Bravais lattice determined by kpoints.x. That means pw.x determines > the symmetry among 7 crystal systems. > > But, now I have a another question about bands.x. > In the instruction of bands.x, it says: > Presently it can calculate: >(a) The expectation value of the spin operator on each spinor > wave-function. >(b) The symmetry properties of each wavefunction. > The instruction of parameter "lsym" says: > If .true. the bands are classified according to the irreducible > representations of the small group of k. A file "filband".rap with > the same format of "filband" is written. > > I want to know the symmetry properties obatained by "band.x" is > based on 7 crystal systems, 14 Bravais lattices or 32 point groups. > > Once again, thank you very much ?? > > > Hui Wang > School of physics, Nankai University, Tianjin, China > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20090811/444e9e73/attachment.htm
[Pw_forum] generating k point weights
Dear Stefano Baroni and Gabriele Sclauzero: First of all, thank you very much for your detailed explanation :? I think I fully undertand it. First, the "kpoints.x" reduces the number of k-points according to parameter "ibrav". That means kpoints.x chooses the symmetry among 14 Bravais lattices. Second, the "pw.x" checkes all symmetry operations within a given Bravais lattice determined by kpoints.x. That means pw.x determines the symmetry among 7 crystal systems. But, now I have a another question about bands.x. In the instruction of bands.x, it says: Presently it can calculate: (a) The expectation value of the spin operator on each spinor wave-function. (b) *The symmetry properties of each wavefunction*. The instruction of parameter "lsym" says: If .true. the bands are classified according to the irreducible representations of the small group of k. A file "filband".rap with the same format of "filband" is written. I want to know the symmetry properties obatained by "band.x" is based on 7 crystal systems, 14 Bravais lattices or 32 point groups. Once again, thank you very much ?? Hui Wang School of physics, Nankai University, Tianjin, China -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20090811/e6e05ad2/attachment.htm
[Pw_forum] generating k point weights
Dear Gabriele Sclauzero: >Just one additional note of caution: kpoints.x reduces the number of k-points (and compute >weights) according to the symmetry of the bravais lattice only, while the subroutine >kpoint_grid in PW/ used by pw.x takes into account the crystal symmetry (which can be >lower than the lattice symmetry if you have more than one atom per cell or non-collinear >magnetism) I am confused with your statement:"crystal symmetry can be lower than the lattice symmetry if you have more than one atom per cell". Could you explain it more clearly? Or could you give me a simple example? Thank you ?? Hui Wang School of physics, Nankai University, Tianjin, China -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20090810/531940cb/attachment-0001.htm
[Pw_forum] generating k point weights
xirainbow wrote:
> Dear Gabriele Sclauzero:
>
> >Just one additional note of caution: kpoints.x reduces the number of
> k-points (and compute
> >weights) according to the symmetry of the bravais lattice only, while
> the subroutine
> >kpoint_grid in PW/ used by pw.x takes into account the crystal
> symmetry (which can be
> >lower than the lattice symmetry if you have more than one atom per
> cell or non-collinear
> >magnetism)
>
> I am confused with your statement:"crystal symmetry can be lower than
> the lattice symmetry if you have more than one atom per cell".
Maybe I misused the standard terminology.
> Could you explain it more clearly?
Every periodic system can be described by one among the 14 Bravais lattices
plus a
so-called "basis", i.e. a set of atomic position within the unit cell of that
lattice. The
symmetry point group of the lattice is the set of all rotations which leave the
lattice
invariant (which means that it can be mapped to itself with the application of
a
translation of a l.c. of the basis vectors, if needed).
This is the symmetry group given by kpoints.x (which in fact does not ask
anything about
the basis of atoms).
To determine the symmetry of a crystallographic system you have to check which
symmetry
operations leave the system invariant, which means that, after a rotation, each
atom
overlaps with itself or with an equivalent atom (again, modulus a translation
by a lattice
vector).
If you have more than one atom, or your atom is not in the origin an operation
with
transform the lattice into itself may not send all the atoms on top of
equivalent atoms,
hence it is not a symmetry operation.
For some systems (e.g. diamond), you may recover some rotations by applying a
translation
by a fraction of a lattice vector after the rotation.
> Or could you give me a simple example?
Sorry, I don't have a crystallographic example in mind right now, but I can
give you a
practical example of what I've got my hands on at the moment.
In order to simulate monatomic nanowires I use a tetragonal cell (ibrav=6) with
one atom
per cell (along the z axis). The lattice symmetry (point group D_4d) is
maintained also
after checking the atomic basis (although this system in reality as D_{\inf h}
point
group, but this is another story...).
If you adsorb an impurity aside of the wire, e.g. a molecule lying in the xz
plane, the
symmetry of the system will be lowered (C_2v in this case). In fact you will
lose the
inversion symmetry (this halves the number of symmetry operations) and the
rotations along z.
I hope I've not confused you further...
GS
> Thank you ??
>
>
> Hui Wang
> School of physics, Nankai University, Tianjin, China
>
>
>
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
--
o o
| Gabriele Sclauzero, PhD Student |
| c/o: SISSA & CNR-INFM Democritos, |
|via Beirut 2-4, 34014 Trieste (Italy) |
| email: sclauzer at sissa.it |
| phone: +39 040 3787 511 |
| skype: gurlonotturno |
o o
[Pw_forum] generating k point weights
More precisely: the point symmetry of the bravais lattive can be higher than the maximum symmetry of any lattie site in the crystal. For example, the point symmetry of the bravais lattice of the diamond structure is cubic, but no lattice site in the diamond structure has cubic symmetry (actually, each atomic site has tetrahedral symmetry). In this case, cubic symmetry s recovered by associating a fractional lattice translation to certain operation of the cubic group (it is said the the space group of the structure is "non symmorphic" in this case). More generally, it may happen that you simulate a system of low symmetry (a molecule, for instance) with a supercell of higher symmetry (think of using a cubic supercell for symulating an isolated water molecule, for instance) ... SB On Aug 10, 2009, at 4:41 PM, xirainbow wrote: > Dear Gabriele Sclauzero: > > >Just one additional note of caution: kpoints.x reduces the number > of k-points (and compute > >weights) according to the symmetry of the bravais lattice only, > while the subroutine > >kpoint_grid in PW/ used by pw.x takes into account the crystal > symmetry (which can be > >lower than the lattice symmetry if you have more than one atom per > cell or non-collinear > >magnetism) > > I am confused with your statement:"crystal symmetry can be lower > than the lattice symmetry if you have more than one atom per cell". > Could you explain it more clearly? > Or could you give me a simple example? > Thank you ?? > > > Hui Wang > School of physics, Nankai University, Tianjin, China > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum --- Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) La morale est une logique de l'action comme la logique est une morale de la pens?e - Jean Piaget Please, if possible, don't send me MS Word or PowerPoint attachments Why? See: http://www.gnu.org/philosophy/no-word-attachments.html -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20090810/bf370681/attachment.htm
[Pw_forum] generating k point weights
Dear All, Thank you very much for all the help :) Regards, Manoj Srivastava University of Florida Gainesville, FL On Mon, 10 Aug 2009, Gabriele Sclauzero wrote: > Just one additional note of caution: kpoints.x reduces the number of k-points > (and compute > weights) according to the symmetry of the bravais lattice only, while the > subroutine > kpoint_grid in PW/ used by pw.x takes into account the crystal symmetry > (which can be > lower than the lattice symmetry if you have more than one atom per cell or > non-collinear > magnetism) > > HTH > > GS > > Manoj Srivastava wrote: > > Dear Lorenzo, > > Thanks a lot. I will look into the code. In the mean time I found a paper > > which talks about generation of special k points and evaluation of their > > weight. Its by Chadi & Cohen, Phys. Rev. B, 8,5747-5753 (1973). They have > > some examples in it too. > > > > Regards, > > Manoj Srivastava > > University of Florida, > > Gainesville, FL > > > > On Mon, 3 Aug 2009, Lorenzo Paulatto wrote: > > > >> In data 31 luglio 2009 alle ore 16:25:39, Manoj Srivastava > >> ha scritto: > >> > >>> Dear All, > >>> I was wondering if someone can tell me, how to generate k point weights > >>> in the BZ. Reference of a paper would be great! > >> Dear Manoj, > >> you can find the algorithm tha tgenerates points and weights in > >> pwtools/kpoints.f > >> The obvious reference is the original article from Monkhorst and Pack: > >> Phys. Rev. B 13, 5188 - 5192 (1976), although I don't know if they give an > >> > >> explicit formulation for the weights there (weights depend on how many > >> symmetry-equivalent copies of a point are present in the set, not on the > >> generation algorithm). > >> > >> cheers > >> > >> > >> -- > >> Lorenzo Paulatto > >> SISSA & DEMOCRITOS (Trieste) > >> phone: +39 040 3787 511 > >> skype: paulatz > >> www: http://people.sissa.it/~paulatto/ > >> > >> *** save italian brains *** > >> http://saveitalianbrains.wordpress.com/ > >> ___ > >> Pw_forum mailing list > >> Pw_forum at pwscf.org > >> http://www.democritos.it/mailman/listinfo/pw_forum > >> > > > > ___ > > Pw_forum mailing list > > Pw_forum at pwscf.org > > http://www.democritos.it/mailman/listinfo/pw_forum > > > > -- > > > o o > | Gabriele Sclauzero, PhD Student | > | c/o: SISSA & CNR-INFM Democritos, | > |via Beirut 2-4, 34014 Trieste (Italy) | > | email: sclauzer at sissa.it | > | phone: +39 040 3787 511 | > | skype: gurlonotturno | > o o > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >
[Pw_forum] generating k-point weights
> > -- > > Message: 1 > Date: Mon, 03 Aug 2009 13:47:54 +0200 > From: "Lorenzo Paulatto" > Subject: Re: [Pw_forum] generating k point weights > To: "PWSCF Forum" > Message-ID: > Content-Type: text/plain; charset=utf-8; format=flowed; delsp=yes > > In data 31 luglio 2009 alle ore 16:25:39, Manoj Srivastava > ha scritto: > >> Dear All, >> I was wondering if someone can tell me, how to generate k point weights >> in the BZ. Reference of a paper would be great! > > Dear Manoj, > you can find the algorithm tha tgenerates points and weights in > pwtools/kpoints.f > The obvious reference is the original article from Monkhorst and Pack: Phys. Rev. B 13, 5188 - 5192 (1976), although I don't know if they give an > explicit formulation for the weights there (weights depend on how many symmetry-equivalent copies of a point are present in the set, not on the generation algorithm). > > cheers > > Hello, I would like to point out that pwscf generates k-points slightly differently from the way it was done by Monkhorst and Pack in their original paper. For them, the k-point grid either included or did not include Gamma (zone center) depending on whether the number of divisions was odd or even. However, in PWscf, 'unshifted' grids always include Gamma, and 'shifted' ones do not, regardless of whether the number of divisions is odd or even. To get weights: you have to see how many k points in the full BZ are equivalent to the given point in the IBZ. I have a slide illustrating this in my recent talk at the UCSB Q-E summer school, see my first lecture, slides available at http://www.quantum-espresso.org/wiki/index.php/QESB09 Shobhana Narasimhan Theoretical Sciences Unit Jawaharlal Nehru Centre for Advanced Scientific Research Bangalore
[Pw_forum] generating k point weights
In data 31 luglio 2009 alle ore 16:25:39, Manoj Srivastava ha scritto: > Dear All, > I was wondering if someone can tell me, how to generate k point weights > in the BZ. Reference of a paper would be great! Dear Manoj, you can find the algorithm tha tgenerates points and weights in pwtools/kpoints.f The obvious reference is the original article from Monkhorst and Pack: Phys. Rev. B 13, 5188 - 5192 (1976), although I don't know if they give an explicit formulation for the weights there (weights depend on how many symmetry-equivalent copies of a point are present in the set, not on the generation algorithm). cheers -- Lorenzo Paulatto SISSA & DEMOCRITOS (Trieste) phone: +39 040 3787 511 skype: paulatz www: http://people.sissa.it/~paulatto/ *** save italian brains *** http://saveitalianbrains.wordpress.com/
[Pw_forum] generating k point weights
Dear Lorenzo, Thanks a lot. I will look into the code. In the mean time I found a paper which talks about generation of special k points and evaluation of their weight. Its by Chadi & Cohen, Phys. Rev. B, 8,5747-5753 (1973). They have some examples in it too. Regards, Manoj Srivastava University of Florida, Gainesville, FL On Mon, 3 Aug 2009, Lorenzo Paulatto wrote: > In data 31 luglio 2009 alle ore 16:25:39, Manoj Srivastava > ha scritto: > > > Dear All, > > I was wondering if someone can tell me, how to generate k point weights > > in the BZ. Reference of a paper would be great! > > Dear Manoj, > you can find the algorithm tha tgenerates points and weights in > pwtools/kpoints.f > The obvious reference is the original article from Monkhorst and Pack: > Phys. Rev. B 13, 5188 - 5192 (1976), although I don't know if they give an > explicit formulation for the weights there (weights depend on how many > symmetry-equivalent copies of a point are present in the set, not on the > generation algorithm). > > cheers > > > -- > Lorenzo Paulatto > SISSA & DEMOCRITOS (Trieste) > phone: +39 040 3787 511 > skype: paulatz > www: http://people.sissa.it/~paulatto/ > > *** save italian brains *** > http://saveitalianbrains.wordpress.com/ > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >
[Pw_forum] generating k point weights
Dear All, I was wondering if someone can tell me, how to generate k point weights in the BZ. Reference of a paper would be great! Regards, Manoj
