<div dir="ltr">Dear Cameron, <div><br></div><div>I have a lot of experience with Titanium. I noticed a couple of mistakes in your input file.</div><div><br></div><div>1) You need to use smearing for metals (see this <a href="http://caribeictp.uis.edu.co/lectures/R.Gebauer/Gebauer_Course2_KpointsMetals.pdf">http://caribeictp.uis.edu.co/lectures/R.Gebauer/Gebauer_Course2_KpointsMetals.pdf</a>)</div><div>2) You are using an ultrasoft pseudopotential, so you also need to specify 'ecutrho', which is 8*ecutwfc</div><div>3) It is better to use gamma centered k-mesh for hexagonal systems</div><div><br></div><div>I also recommend you do convergence studies w.r.t energy cutoffs, smearing and k-mesh</div><div><div style="font-size:12.8px"><br></div><div style="font-size:12.8px">%%%%% SCF %%%%%</div><div style="font-size:12.8px"><div> 1 &control</div><div> 2 calculation='scf',</div><div> 3 restart_mode='from_scratch',</div><div> 4 outdir='/oasis/scratch/cjfoss/temp_project/out_ti', </div><div> 5 pseudo_dir='/home/cjfoss/espresso-5.1/pseudo',</div><div> 6 prefix='TiPHv4'</div><div> 7 /</div><div> 8 &system</div><div> 9 ibrav=0,</div><div> 10 celldm(1)=5.507258084,</div><div> 11 celldm(3)=1.587457, -------------------> This flag will be ignored for ibrav=0 </div><div> 12 nat=2, ntyp=1,</div><div> 13 ecutwfc=100.0 -------------> This cutoff is very high for this pseudopotential (I use 40 Ry for thsi pseudopotential). If you are using an ultrasoft pseudopotential, you also need to mention ecutrho = 8*ecutwfc</div><div> 14 /</div><div> 15 &electrons</div><div> 16 mixing_beta=0.7,</div><div> 17 conv_thr = 1.0d-12</div><div> 18 /</div><div> 19 ATOMIC_SPECIES</div><div> 20 Ti 47.867 Ti.pw91-nsp-van.UPF -----------> Ultrasoft pseudopotential</div><div> 21 ATOMIC_POSITIONS {crystal}</div><div> 22 Ti 0.33333333 0.66666666 0.25</div><div> 23 Ti 0.66666666 0.33333333 0.75</div><div> 24 K_POINTS automatic</div><div> 25 7 7 7 1 1 1 --------------------------------> I use 18 18 12 0 0 0 here, but i recommend you do your own convergence studies.</div><div> 26 CELL_PARAMETERS (alat)</div><div> 27 1.000043369 0.000000000 0.000000000</div><div> 28 -0.500021685 0.866062962 0.000000000</div><div> 29 0.000000000 0.000000000 1.615221757</div><div> 30</div></div></div><div><br></div><div>Hope this helps</div><div><br></div><div>Krishnamohan</div><div><br></div><div><br></div><div><br></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jul 19, 2016 at 6:06 AM, Cameron Foss <span dir="ltr"><<a href="mailto:cjfoss@umass.edu" target="_blank">cjfoss@umass.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hello all,<div><br></div><div>I am trying to simulate phonons in titanium with espresso-5.1. My results so far seem to show the presence of soft phonons (negative frequencies) an indicator of material instability and possibly the initiation of phase transitions (EPL, 95 (2011) 18002) as well as some other irregularities in the shape of the branches.</div><div><br></div><div>To my knowledge, different pseudopotentials can have different equilibrium lattice constants for a given material. Hence I perform vc-relax simulations and update the lattice constant until the variations seen in the lattice vectors is below .05%. I then use the relaxed lattice vectors and atomic positions in the scf (pw.x) simulation and proceed with a phonon (ph.x) simulation. </div><div><br></div><div>I have generated my scf input file based off of the following <b>Phys. Scr. 83 (2011) 065603</b> and <b>Condensed Matter Physics, 2011, Vol. 14, No 2, 23601: 1–7.</b><br></div><div><b><br></b></div><div>Below are the input files for the scf and phonon simulations. The vc-relax simulation is excluded because its input parameters are the same as the scf simulation (MP grid, conv_thr, ecutwfc, etc). Lastly, the bfgs scheme is used in the vc-relax calculation.</div><div><br></div><div>%%%%% SCF %%%%%</div><div><div> 1 &control</div><div> 2 calculation='scf',</div><div> 3 restart_mode='from_scratch',</div><div> 4 outdir='/oasis/scratch/cjfoss/temp_project/out_ti', </div><div> 5 pseudo_dir='/home/cjfoss/espresso-5.1/pseudo',</div><div> 6 prefix='TiPHv4'</div><div> 7 /</div><div> 8 &system</div><div> 9 ibrav=0,</div><div> 10 celldm(1)=5.507258084,</div><div> 11 celldm(3)=1.587457,</div><div> 12 nat=2, ntyp=1,</div><div> 13 ecutwfc=100.0</div><div> 14 /</div><div> 15 &electrons</div><div> 16 mixing_beta=0.7,</div><div> 17 conv_thr = 1.0d-12</div><div> 18 /</div><div> 19 ATOMIC_SPECIES</div><div> 20 Ti 47.867 Ti.pw91-nsp-van.UPF</div><div> 21 ATOMIC_POSITIONS {crystal}</div><div> 22 Ti 0.33333333 0.66666666 0.25</div><div> 23 Ti 0.66666666 0.33333333 0.75</div><div> 24 K_POINTS automatic</div><div> 25 7 7 7 1 1 1</div><div> 26 CELL_PARAMETERS (alat)</div><div> 27 1.000043369 0.000000000 0.000000000</div><div> 28 -0.500021685 0.866062962 0.000000000</div><div> 29 0.000000000 0.000000000 1.615221757</div><div> 30</div></div><div><br></div><div>%%%%% PH %%%%%</div><div><div> 1 PHONONS IN TITANIUM</div><div> 2 &inputph</div><div> 3 tr2_ph=1.0d-14,</div><div> 4 max_seconds=129600,</div><div> 5 prefix='TiPHv4',</div><div> 6 ! recover=.true.</div><div> 7 ldisp=.true.,</div><div> 8 nq1=7, nq2=7, nq3=7,</div><div> 9 amass(1)=47.867,</div><div> 10 outdir='/oasis/scratch/cjfoss/temp_project/out_ti',</div><div> 11 fildyn='ti.dyn',</div><div> 12 /</div></div><div><br></div><div>My BZ traversal moves along the path G-K-M-G-A, where G stands for the Gamma zone-center point. The symmetry points used are K=(2/3,0,0) ; M=(0.5,-1/(2*sqrt(3)),0) ; A=(0,0,a/(2c)) ; and G=(0,0,0). I am confident in these points since I have used them to get a proper dispersion of AlN but include them here for completeness.</div><div><br></div><div>It is unclear to me whether the soft phonon modes are a result of my celldm(3) being different than the v3 z-component in CELL_PARAMETERS or if I am missing a parameter that is pertinent to simulating phonons in metals? Any help is appreciated.</div><div><br></div><div>Best Regards,</div><div>Cameron</div><div><br></div></div>
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<a href="http://pwscf.org/mailman/listinfo/pw_forum" rel="noreferrer" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a><br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><font face="comic sans ms, sans-serif" color="#999999"><b>Krishnamohan Thekkepat</b></font><div><font face="comic sans ms, sans-serif" color="#999999"><b>Research Associate</b></font></div><div><font color="#999999"><b><span style="font-family:'comic sans ms',sans-serif">Indo-Korea Science and Technology Center, Bangalore, India</span></b></font></div><div><b><font face="comic sans ms, sans-serif"><br></font></b></div><div><font color="#9999ff" face="comic sans ms, sans-serif"><span style="font-size:12px">“We shall not cease from exploratio</span><span style="font-size:12px">n, and the end of all our exploring will be to arrive where we started and know the place for the first time.”- T.S Eliot</span></font></div></div></div></div></div></div></div>
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