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) isspecified? If anybody has any information about this I would highlyappreciate.“fltau” option of matdyn gives atomic positions only for 1 cell andnot for N1xN2xN3 supercell.Apparently, there are some tricks… for example, here one has some IFCsfor 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 haveto be shuffled2. second, it seems SUBROUTINE setupmat and frc_blk is the right placeto 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 Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum

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