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 >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
