[Pw_forum] about phonon calculation

[Adam Jacobsson]

Hi! 
 
Regarding k-points: The program will use symmetry to reduce the amount of used k-points as much as possible, i.e. those found in the irreducible BZ. Those might just be 60 in your case.   
 
Regarding phonons: You need to change occupation from smearing. That one is appropriate for metals but not for insulators. Use 'fixed' instead. Check the documentation for details. 
 
Best,
Adam Jacobsson



Date: Mon, 22 Dec 2008 16:05:50 +0530From: lataprem29 at gmail.comTo: pw_forum at pwscf.orgSubject: [Pw_forum] about phonon calculationDear Pwscf users,Here I am sending you the input file of Li2S (large band gap semi-conductor) for scf and phonon calculations. I have some queries regarding this1. For electronic calculation i am using 8x8x8 k-points which results in only 60 points. Is it enough to do correct electronic calculations?With these 60 points only, I calculated the bulk mobulus and the equilibrium lattice constants, which matches well with the experiment and other theoritical results.2. For phonon calculation, I didnt get the LO-TO splitting. Can you please tell me what more parameters i will use to get the splitting. I set epsil .true., but it gives the error       from phq_readin : error #         1     no elec. field with metalsAny suggestion is highly apperciable li2s.scf.in&CONTROL               calculation = 'scf' ,              restart_mode = 'from_scratch' ,                    outdir = './OUT',                pseudo_dir = '/root/bipul/espresso-4.0.1/pseudo/Li2S',                   prefix = 'Li2S',             etot_conv_thr = 1.0d-5 ,             forc_conv_thr = 1.0d-4 ,                   tstress = .true. ,                   tprnfor = .true. ,                        dt = 80 / &SYSTEM                     ibrav = 2,                 celldm(1) =  10.72700,                       nat = 3,                      ntyp = 2 ,                   ecutwfc = 32,                   ecutrho = 600,                  occupations = 'smearing' ,                    smearing = 'methfessel-paxton',                   degauss = 0.01 / &ELECTRONS               mixing_beta = 0.5 ,            conv_thr =  1.0d-8           diagonalization = 'david' , / &IONS /ATOMIC_SPECIES S   32.066  S.pw91-van_ak.UPF Li  6.914   Li.pw91-s-van_ak.UPFATOMIC_POSITIONS (crystal)S  0.0 0.0 0.0Li 0.25 0.25 0.25Li 0.75 0.75 0.75K_POINTS automatic  8 8 8 1 1 1li2s.ph.inphonons of Li2S &inputph ! recover =.true.,  tr2_ph=1.0d-12,  alpha_mix(1)=0.6,  prefix='Li2S', ! fildvscf='li2sdv',  amass(1)=32.066,  amass(2)=6.941,  outdir='./OUT',  fildyn='li2s.dyn', ! elph=.true., ! trans=.true.,  ldisp=.true.  nq1=4, nq2=4, nq3=4 /-- Premlata PanditPh.d. student,Barkatullah university,Bhopal 462026,MP, India 
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