OK, got it... That's why it worked when I chose nr1=nr2=nr3=128 - the code uses the symmetries including translations in this case as nr1=nr3. Similarly I should choose at least nk1=nk3, but as the 1st and the 2nd lattice vectors are nearly the same length I should probably use nk1=nk2=nk3.
Thanks Thomas On 08/09/2016 12:53 PM, stefano de gironcoli wrote: > it does not look so much longer than the other to me ... > Anyhow the point is that a grid in order to respect the symmetry must > transform into itself under symmetry operations and yours does not > satisfy this condition for reflexion x -> -x, z -> -z and rotations of > pi around z ... > > unless nk1=nk3 > > for the fft grid ... I would try to keep nr1=nr3 for the same reason. > actually my suggestion was based on a real-space argument but I'm pretty > sure it is valid in reciprocal space too. > > stefano > > On 09/08/2016 11:34, Thomas Brumme wrote: >> Thanks for the suggestion Stefano! >> >> Yet, lattice vector 3 is in my cell the largest and correspondingly nk3 >> must be larger than nk1=nk2, or? That's why I choose 10 10 6 (even if I >> might have to increase nk3 slightly). >> >> Or do I miss something? I meanwhile also played with the cutoff of the >> wave functions (i.e. finding also an fft mesh which can be used with the >> symmetries which include a translation) but even if the fft mesh is >> 96x96x120 the symmetries which include the translation are neglected. >> I'll try with 96x96x128... >> >> Thomas >> >> On 08/09/2016 02:59 AM, stefano de gironcoli wrote: >>> I think that given your Bravais lattice nk3 must be equal to nk1 >>> so >>> 10 nk2 10 0 0 0 >>> or >>> 6 nk2 6 0 0 0 >>> should be fine >>> >>> 10 nk2 6 0 0 0 >>> is not >>> >>> the automatic unfolding of a grid generate additional points but this >>> does not mean they form a regular grid. think about what happens for an >>> hexagonal lattice with a shifted grid. >>> >>> stefano >>> >>> On 08/08/2016 17:51, Thomas Brumme wrote: >>>> Dear all, >>>> >>>> I want to calculate the phonon frequencies on a regular q mesh specified >>>> by using >>>> ldisp=.true. and the nq1, nq2, nq3 variables. Yet, I always get the error >>>> >>>> q-mesh breaks symmetry >>>> >>>> even if the grid has the same dimensions as the k mesh in the PWscf >>>> calculation. >>>> This is weird as the q mesh is exactly the same as the k mesh, which was >>>> created >>>> by applying the symmetries to a regular grid. The system is LCO and the >>>> input for >>>> PWscf (in the reduced cell) is: >>>> >>>> &control >>>> calculation = 'scf', >>>> restart_mode = 'from_scratch', >>>> prefix = 'LCO', >>>> pseudo_dir = './', >>>> outdir = './tmp/', >>>> nstep = 300, >>>> wf_collect = .true., >>>> / >>>> &system >>>> ibrav = 0, >>>> nat = 14, >>>> ntyp = 3, >>>> ecutwfc = 200, >>>> occupations = 'smearing', >>>> smearing = 'gauss', >>>> degauss = 0.01, >>>> nspin = 2, >>>> starting_magnetization(3) = 0.02, >>>> nr1 = 128, >>>> nr2 = 128, >>>> nr3 = 128, >>>> / >>>> &electrons >>>> electron_maxstep = 250, >>>> diagonalization = 'cg', >>>> conv_thr = 1.0d-10, >>>> / >>>> CELL_PARAMETERS (angstrom) >>>> 5.261112503 0.000000000 0.000000000 >>>> 0.000000000 5.330947322 0.000000000 >>>> -2.630556252 -0.000000000 6.548827231 >>>> ATOMIC_SPECIES >>>> La 138.90547 La1.UPF >>>> O 15.999 O.pz-n-mt.UPF >>>> Cu 63.546 Cu1.UPF >>>> K_POINTS automatic >>>> 10 10 6 0 0 0 >>>> ATOMIC_POSITIONS (crystal) >>>> ... >>>> >>>> I defined the FFT grid by hand since then the code does not drop the >>>> symmetries >>>> including fractional translations... Could this be the problem? Or that >>>> I did choose >>>> a FFT grid which has the same number of points in x/y/z directions? Or >>>> could this >>>> be due to a similar problem" as in hexagonal crystals where shifting the >>>> k mesh >>>> away from Gamma is a bad idea? Or is there an obvious error in my input >>>> for ph.x: >>>> >>>> &inputph >>>> tr2_ph = 1.0d-18, >>>> prefix = 'LCO', >>>> amass(1) = 138.90547, >>>> amass(2) = 15.999, >>>> amass(3) = 63.546, >>>> outdir = './tmp/', >>>> fildyn = 'LCO.dynG', >>>> ldisp=.true., >>>> nq1=10, nq2=10, nq3=6, >>>> fildvscf = 'LCO.dvscf', >>>> verbosity = 'high', >>>> / >>>> >>>> I searched the archive however I couldn't find a solution to my problem. >>>> Thus, any >>>> help would be very much appreciated :) >>>> >>>> Regards >>>> >>>> Thomas >>>> >>> _______________________________________________ >>> 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 -- Dr. rer. nat. Thomas Brumme Max Planck Institute for the Structure and Dynamics of Matter Luruper Chaussee 149 22761 Hamburg Tel: +49 (0)40 8998 6557 email: thomas.bru...@mpsd.mpg.de _______________________________________________ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum