Great. Now I can add a fourth link to point 7.7 of the FAQ, http://www.quantum-espresso.org/faq/phonons/
P. On Thu, 2014-11-06 at 18:54 +0100, stefano de gironcoli wrote: > dear Alexander, > > the grid correspond to a 8x8x8 supercell (or rather to the FFT of > a 8x8x8 q-point grid ... which is the same) > > atomic pairs are specified by the indices of the two atoms in the > unit cell plus the direct lattice vector connecting the two cells in > which they are located with two important details to be considered > 1) the origin is the 1,1,1 element of the list > 2) the IFC are obtained by a FFT from the dynamical matrices of > the q-point grid and are therefore written assuming 8 8 8 periodicity > (in the present case) > the corresponding relevant real space vectors vectors are > therefore given by > r(i) = (n1-1)*at(i,1)+(n2-1)*at(i,2)+(n3-1)*at(i,3) + their > periodic refolding to points nearest the origin > a few examples should clarify: > 1 1 1 -> r = 0 > 2 1 1 -> r = a1 > 8 1 1 -> r = -a1 > > the routine weight play the fundamental role of trimming the > vector in such a way the only the points inside the wigner-seitze > cell of the supercell contribute > weight (r) = 1 if r is inside the WS cell > weight (r) = 0 if r is ouside the WS cell > weight (r) = 1/(n+1) if r is on the surface of the WS cell where > n is the number of planes that pass through it > > stefano > > On 11/06/2014 06:14 PM, Kvasov Alexander wrote: > > > Dear All, > > > > > > > > My question is: how the supercell (which is used by q2r and matdyn) > > is specified? If anybody has any information about this I would > > highly appreciate. > > > > “fltau” option of matdyn gives atomic positions only for 1 cell and > > not for N1xN2xN3 supercell. > > > > Apparently, there are some tricks… for example, here one has some > > IFCs for 8x8x8 grid of SrTiO3 > > > > ... > > > > 8 8 8 > > > > 1 1 1 1 > > > > 1 1 1 5.72142674655E-02 > > > > 2 1 1 -1.06343912107E-02 > > > > 3 1 1 1.01649714042E-04 > > > > 4 1 1 4.15611567060E-06 > > > > 5 1 1 -6.46046533014E-06 > > > > 6 1 1 4.15611567060E-06 > > > > 7 1 1 1.01649714042E-04 > > > > 8 1 1 -1.06343912107E-02 > > > > ... > > > > 1. first, IFC values decries with N1 and then increase, so they have > > to be shuffled > > > > 2. second, it seems SUBROUTINE setupmat and frc_blk is the right > > place to look for this > > > > … > > > > DO na=1, nat > > > > DO nb=1, nat > > > > total_weight=0.0d0 > > > > DO n1=-2*nr1,2*nr1 > > > > DO n2=-2*nr2,2*nr2 > > > > DO n3=-2*nr3,2*nr3 > > > > ! > > > > ! SUM OVER R VECTORS IN THE SUPERCELL - VERY VERY > > SAFE RANGE! > > > > ! > > > > DO i=1, 3 > > > > r(i) = n1*at(i,1)+n2*at(i,2)+n3*at(i,3) > > > > END DO > > > > … > > > > but summation goes from -2N to 2N, which is not clear for me. > > > > 3. what is “weight” in SUBROUTINE setupmat and frc_blk > > > > If anybody could explain what is going on here it would be great! > > > > > > > > > > > > Sincerely yours, > > > > > > > > Alexander Kvasov > > > > Scientist > > > > Ceramics Laboratory (LC) > > > > École Polytechnique Fédérale de Lausanne (EPFL) > > > > > > > > Phone: +41 21 693 5805 > > > > Address: > > > > EPFL STI IMX LC > > > > MXD 220 (Bâtiment MXD) Station 12 > > > > 1015 Lausanne, Switzerland > > > > > > > > > > > > > > _______________________________________________ > > Pw_forum mailing list > > [email protected] > > http://pwscf.org/mailman/listinfo/pw_forum > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
