Sorry: Highest (not lowest converged...) On Tue, Dec 12, 2017 at 10:43 AM, Sitangshu Bhattacharya < [email protected]> wrote:
> Dear Francesco, > > As far as I understood, smearing is probably creating you a problem. This > is preferably used when you deal with metallic system. Try with "occupation > = fixed". The other thing could be due to the ecutwfc. You need to check > this cut off with respect to each element and take the lowest converged one > for quick results. This also depends on the type of pseudo you are using. > Relaxation with 20 20 1 is good, but so large sampling is not required as > it is easy to converge the phonon frequencies. 12 12 1 or 14 14 1 scf will > do the job, even in my case 6 6 1 does this. You may also use this to > generate less number of regular q-points along the BZ route. Specifically > do also check with any double prime frequencies (like A" or so) in your > report file. These are bad for single layers. > Hope this will help you.. > > Regards, > Sitangshu > > On Tue, Dec 12, 2017 at 3:51 AM, Francesco Delodovici < > [email protected]> wrote: > >> Hello all! >> I have some troubles with phonons in two dimensional hexagonal Boron >> Nitride, and I am looking for some hints: >> >> 1) the out-of-plane acoustic branch at low wave vector is not quadratic, >> istead is linear. >> At a first glance, I thought this could be related to some residual >> forces, but I performed two successive vc-relax calculations >> and they are 0.000000 according to the output. There is some residual >> pressure on z axis, but I suppouse it is related to the constrain >> on the c primitive vector (through the flag cell_dofree = '2Dxy' >> ). >> I doubt that this is due to some periodic images interaction, because the >> cell is 20 A in the direction perpendicular to the layer plane. >> >> I also increased the q-point mesh from 6x6x1 up to 10x10x1 in the ph.x >> input. In the latter case the out-of-plane acoustic branch turns out >> to have a parabolic-like behaviour around Gamma but with opposite >> concavity. >> >> 2) Since I don't include the flag epsil='true' there is no LO-TO >> splitting, but the slope of the LO branch is vanishing at Gamma >> and it shouldn't. Any chance that some option exists to obtain correct >> behaviour of otpical phonons in 2D for vanishing wave vector? >> >> I'm using quantum espersso v6.0. >> >> Find attached below the input file for vc-relax and phonons. >> >> >> Any suggestion will be appreciated, >> thank you! >> >> Francesco Delodovici, Phd Student >> Università degli studi di Milano >> >> >> ############ VC RELAX ################### >> &CONTROL >> title = 'hbn' , >> calculation = 'vc-relax' , >> restart_mode = 'from_scratch' , >> outdir = '/localdisk1/delodovici/' , >> pseudo_dir = '~/Pseudop/' , >> prefix = 'hbn' , >> forc_conv_thr = 1D-8 , >> etot_conv_thr = 1D-8 , >> wf_collect = .false. , >> / >> &SYSTEM >> ibrav = 4 , >> celldm(1) = 4.695926777902829 , >> celldm(3) = 8.048362859199854 , >> nat = 2 , >> ntyp = 2 , >> ecutwfc = 50 , >> ecutrho = 200 , >> occupations = 'smearing' , >> smearing = 'gaussian' , >> degauss = 2e-4 , >> nspin = 1 , >> / >> &ELECTRONS >> conv_thr = 1.0d-9 >> / >> &IONS >> ion_dynamics = 'bfgs' >> / >> &CELL >> cell_dynamics = 'bfgs' >> cell_dofree = '2Dxy' >> / >> ATOMIC_SPECIES >> N 14.007 N.pz-rrkjus.UPF >> B 10.810 B.pz-n-rrkjus_psl.0.1.UPF >> >> ATOMIC_POSITIONS crystal >> B 0.000000 0.000000 0.000000 >> N 0.333333 0.666666 0.000000 >> >> K_POINTS automatic >> 20 20 1 0 0 0 >> >> ################################################ >> ############### PHONONS ################## >> >> phonons of hBN >> &inputph >> tr2_ph=1.0d-14, >> prefix='hbn', >> amass(1)=14.007, >> amass(2)=10.810, >> outdir='/localdisk1/delodovici', >> fildyn='phonons.dyn', >> ldisp=.true., >> nq1=10, >> nq2=10, >> nq3=1, >> / >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > > -- > ********************************************** > Sitangshu Bhattacharya (সিতাংশু ভট্টাচার্য), Ph.D > Assistant Professor, > Room No. 2221, CC-1, > Nanoscale Electro-Thermal Laboratory, > Department of Electrical and Communication Engineering, > Indian Institute of Information Technology-Allahabad > Uttar Pradesh 211 012 > India > Telephone: 91-532-2922000 Extn.: 2131 > Web-page: http://profile.iiita.ac.in/sitangshu/ > Institute: http://www.iiita.ac.in/ > > -- ********************************************** Sitangshu Bhattacharya (সিতাংশু ভট্টাচার্য), Ph.D Assistant Professor, Room No. 2221, CC-1, Nanoscale Electro-Thermal Laboratory, Department of Electrical and Communication Engineering, Indian Institute of Information Technology-Allahabad Uttar Pradesh 211 012 India Telephone: 91-532-2922000 Extn.: 2131 Web-page: http://profile.iiita.ac.in/sitangshu/ Institute: http://www.iiita.ac.in/
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