Dear Prof. Postnikov, Special thanks again for your kind and prompt response.
(i) The q-paths in input 2 must be rotated by 45 degrees to maintain consistency with the paths in input 1. I would like to kindly know the axis about which the rotation should be performed. (ii) Regarding your suggestion of using the lattice vectors [1/2 -1/2 0], [1/2 1/2 0], [0 0 1], I can't quite figure out why the q-paths will be the same as the q-paths for input 1. The primitive FCC lattice vectors in input 1 are [1/2 1/2 0], [1/2 0 1/2], and [0 1/2 1/2] (with an angle of 60 degrees between each pair of lattice vectors). The angle between the lattice vectors you proposed is 90 degrees for each pair. I'm having a difficulty grasping how this new set of lattice vectors yields the same q-paths as input 1. Any further explanation would be highly appreciated. Thank you very much Professor. On Fri, Dec 30, 2022 at 5:12 PM Andrei Postnikov < andrei.postni...@univ-lorraine.fr> wrote: > Dear Francisco, > so your AFM structure is of CuAu type. This is fine but of course > this is not the only AFM structure possible (and I don't know whether it is > realistic at all, but this of course depends on your objectives). > Now, if you want the q-path to be the same in your two settings, > you should consider that the second one is rotated by 45 degrees. > That is, if you choose the Gamma->X direction || [010] in the first > setting > it must be || [110] in the second setting, with the lattice vectors you > use. > Otherwise define the lattice vectors as [1/2 -1/2 0], [1/2 1/2 0], [0 0 1] > with the same lattice parameter as in the first setting > and enjoy the same coordinates of q points (cartesian, in terms of pi/a) > in both settings. > > Best regards > > Andrei > > > ----- Le 31 Déc 22, à 0:24, garcia ff 000 <garcia.ff....@gmail.com> a > écrit : > > Dear Prof. Postnikov, > > Many thanks and appreciation for your response. I believe I found a > solution to my problem but I want to run it by you. > > First, an FCC cell with 2 unique atoms is equivalent to a tetragonal cell > (this is the smallest unit cell to model antiferromagnetism). > > Using the website > https://urldefense.com/v3/__https://www.materialscloud.org/work/tools/seekpath__;!!D9dNQwwGXtA!RtHnhiKf-1Tr0ZJZ17JGCt-WslBldkrwcANZ1KZuejXMskHtY6-_llZSytEsPLSiAktiz7DhWg1EBpjE-NmrWg$ > , the > high symmetry points in the Brillouin zone are as follows (each set of > points is scaled by the corresponding pi/a): > > Standard FCC primitive cell: Gamma (0,0,0), X(0,2,0), K(1.5,1.5,0), > W(1,2,0), L(1,1,1) > > 2-atom tetragonal cell: Gamma(0,0,0), X(0,1,0), M(1,1,0), R(0,1,0.707107), > A(1,1,0.707107), Z(0,0,0.707107). > > With this information, I believe the two Vibra inputs below, one for the > primitive FCC cell and the other for 2-atom tetragonal cell, are formally > equivalent (the last two k-points in each case, i.e. L and M, is what I'm a > bit unsure about). > > > Thank you very much for your kindness & happy holidays. > > > > (A) Primitive FCC cell: > > NumberOfAtoms 1 > > #Lattice parameters > LatticeConstant 3.47 Ang > %block LatticeVectors > 0.500000 0.500000 0.000000 > 0.500000 0.000000 0.500000 > 0.000000 0.500000 0.500000 > %endblock LatticeVectors > > #Atomic positions > AtomicCoordinatesFormat Fractional > %block AtomicCoordinatesAndAtomicSpecies > 0.000000 0.000000 0.000000 1 54.938 > %endblock AtomicCoordinatesAndAtomicSpecies > > #High symmetry Brillouin zones points scaled by pi/a: Gamma (0,0,0), > X(0,2,0), K(1.5,1.5,0), W(1,2,0), L(1,1,1) > > BandLinesScale pi/a > %block BandLines > 1 0.000 0.000 0.000 \Gamma > 30 0.000 2.000 0.000 X > 30 2.000 2.000 2.000 \Gamma > 30 1.000 1.000 1.000 L > %endblock BandLines > > > > (B) 2-atom tetragonal cell to model antiferromagnetism (this is double the > volume of the FCC primitive cell) > > NumberOfAtoms 2 > > #Lattice parameters > LatticeConstant 2.453660531 Ang #[this is the FCC lattice constant > divided by sqrt(2)] > %block LatticeVectors > 1.000000 0.000000 0.000000 > 0.000000 1.000000 0.000000 > 0.000000 0.000000 1.414213562 > %endblock LatticeVectors > > #Atomic positions > AtomicCoordinatesFormat Fractional > %block AtomicCoordinatesAndAtomicSpecies > 0.000000 0.000000 0.000000 1 54.938 > 0.500000 0.500000 0.500000 1 54.938 > %endblock AtomicCoordinatesAndAtomicSpecies > > #High symmetry Brillouin zones points scaled by pi/a: Gamma(0,0,0), > X(0,1,0), M(1,1,0), R(0,1,0.707107), A(1,1,0.707107), Z(0,0,0.707107) > > BandLinesScale pi/a > %block BandLines > 1 0.000 0.000 0.000 \Gamma > 30 0.000 1.000 0.000 X > 30 1.000 1.000 1.000 \Gamma > 30 2.000 2.000 2.000 M > %endblock BandLines > > > > On Thu, Dec 29, 2022 at 3:34 PM Andrei Postnikov < > andrei.postni...@univ-lorraine.fr> wrote: > >> Dear Francisco, >> it is difficult to give a useful advice on the basis of very limited >> information you provide, >> but my impression is that your problems are not obviously related with >> Vibra. >> Some questions: >> 1. What (magnetic) structure are you modelling? How comes you have four >> atoms per AFM unit cell? >> Can there be two? >> 2. Is electronic structure (and band dispersions) correct, prior to any >> phonons? >> 3. What means "incorrect phonon dispersion"? Do you have problems with >> crystallography / >> choosing the q-path, or is your calculation basically wrong? >> 4. With 4 atoms as you use it so far, the Gamma phonon calculation would >> yield >> 9 modes, which would map genuine zone-center and zone-boundary modes. >> Do they come out reasonably? >> >> To your problem: >> "Basically I want to alter the band lines in input 2 so that they are >> equivalent to the band lines in input 1" - >> you have >> BandLinesScale pi/a >> in both inputs, the same lattice parameter, and the same definition of >> path. >> So if everything is correctly read, you must get the same Cartesian >> q-path in both cases. >> Either this is not so and there is something wrong with the input, >> or the paths are identical but your problem is elsewhere. >> >> Best regards >> >> Andrei >> >> >> >> >> >> >> >> >> ----- Le 29 Déc 22, à 0:40, garcia ff 000 <garcia.ff....@gmail.com> a >> écrit : >> >> Dear Users, >> >> I have appended 2 Vibra inputs below for computing the phonon dispersion >> for FCC Mn. >> >> Input 1 works fine as it gives the expected band shapes for the >> dispersion (but the frequencies are off). The main issue with input 1 is >> that it is not suitable for antiferromagnetic calculations since there is >> only one Mn atom in the primitive cell. >> >> This led me to consider input 2, which has 4 atoms in the unit cell and >> can be used for antiferromagnetic calculations. The issue with input 2 is >> that the bandlines yield an incorrect phonon dispersion. This is what I >> need your help on. Basically I want to alter the band lines in input 2 so >> that they are equivalent to the band lines in input 1. >> >> Any assistance with this, especially from the Vibra authors, would be >> greatly appreciated. >> >> Thank you very much for your kind assistance and God Bless! >> >> Francisco >> >> >> >> >> #INPUT 1 (1 atom in the FCC primitive cell; 125 atoms in Supercell) >> SystemName fccMn_1 >> SystemLabel fccMn_1 >> NumberOfAtoms 1 >> LatticeConstant 3.47 Ang >> %block LatticeVectors >> 0.500000 0.500000 0.000000 >> 0.500000 0.000000 0.500000 >> 0.000000 0.500000 0.500000 >> %endblock LatticeVectors >> >> AtomicCoordinatesFormat Fractional >> %block AtomicCoordinatesAndAtomicSpecies >> 0.000000 0.000000 0.000000 1 54.938 >> %endblock AtomicCoordinatesAndAtomicSpecies >> >> SuperCell_1 2 >> SuperCell_2 2 >> SuperCell_3 2 >> >> AtomicDispl 0.04 Bohr >> >> BandLinesScale pi/a >> %block BandLines >> 1 0.000 0.000 0.000 \Gamma >> 30 2.000 0.000 0.000 X >> 30 2.000 2.000 2.000 \Gamma >> 30 1.000 1.000 1.000 L >> %endblock BandLines >> >> Eigenvectors True >> >> >> >> >> #INPUT 2 (4 atoms in the FCC conventional cell; 108 atoms in Supercell) >> SystemName fccMn_4 >> SystemLabel fccMn_4 >> NumberOfAtoms 4 >> LatticeConstant 3.47 Ang >> %block LatticeVectors >> 1.000000 0.000000 0.000000 >> 0.000000 1.000000 0.000000 >> 0.000000 0.000000 1.000000 >> %endblock LatticeVectors >> >> AtomicCoordinatesFormat Fractional >> %block AtomicCoordinatesAndAtomicSpecies >> 0.000000 0.000000 0.000000 1 54.938 >> 0.500000 0.500000 0.000000 1 54.938 >> 0.500000 0.000000 0.500000 1 54.938 >> 0.000000 0.500000 0.500000 1 54.938 >> %endblock AtomicCoordinatesAndAtomicSpecies >> >> SuperCell_1 1 >> SuperCell_2 1 >> SuperCell_3 1 >> >> AtomicDispl 0.04 Bohr >> >> BandLinesScale pi/a >> # The band lines below are incorrect. >> %block BandLines >> 1 0.000 0.000 0.000 \Gamma >> 30 2.000 0.000 0.000 X >> 30 2.000 2.000 2.000 \Gamma >> 30 1.000 1.000 1.000 L >> %endblock BandLines >> >> Eigenvectors True >> >> >> -- >> SIESTA is supported by the Spanish Research Agency (AEI) and by the >> European H2020 MaX Centre of Excellence >> (https://urldefense.com/v3/__http://www.max-centre.eu/__;!!D9dNQwwGXtA!RtHnhiKf-1Tr0ZJZ17JGCt-WslBldkrwcANZ1KZuejXMskHtY6-_llZSytEsPLSiAktiz7DhWg1EBphmWP8u3g$ >> ) >> >> >
-- SIESTA is supported by the Spanish Research Agency (AEI) and by the European H2020 MaX Centre of Excellence (http://www.max-centre.eu/)
