<div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Dear Dr. Stefano and Dr. Mohr,</blockquote><div><br>Thank you for your comments,
<br><br>Actually I had successfully done phonon dispersion and EPC for Al bulk structure with good results so from now I want to apply for the Al wires structures. Firstly I calculate for 2 atom cell of Al with zigzag wires, and I got 6 phonon modes along q-points and appear some negative frequencies, so I tried to improve my calculation but always appear negative acoustic frequencies (optical branch is no problem) and then I did with 4, 6 atom cell and of course I got 3-n modes but my results still no good like I expect. :(
<br>To check my set up parameters I calculate the same procedure for Al 1D linear chain with 1 and 2 atom cell with hopefully the phonon curves will be the same as I studied theoretically in Solid States books, but it was not :(. So should my calculation be wrong with this system. Could you give me advice about my input parameters? Please keep your eyes my INPUT files (in case of 2 atoms in zigzag chain)
<br><br><a href="http://Al.scf.fit.in">Al.scf.fit.in</a><br><br> &SYSTEM <br> ibrav = 6, <br> celldm(1) = 39.994
, <br> celldm(3) = 0.199762906, <br> nat = 2, <br> ntyp = 1, <br> ecutwfc =
25.D0 , <br> ecutrho = 300, <br> occupations = 'smearing' , <br> degauss = 0.05 , <br> smearing = 'methfessel-paxton' ,
<br> la2F = .true. <br> / <br> &ELECTRONS <br> conv_thr = 1.D-10
, <br> mixing_beta = 0.7D0 , <br> / <br>ATOMIC_SPECIES <br> Al 26.98000 Al.vbc.UPF
<br>ATOMIC_POSITIONS angstrom <br>Al 0.000000000 1.517315647 2.138739361 <br>Al 0.000000000 0.116702849 0.023699809 <br>K_POINTS automatic
<br> 4 4 40 0 0 0 <br><br><a href="http://Al.scf.in">Al.scf.in</a><br><br> &SYSTEM <br> ibrav = 6, <br> celldm(1) =
39.994, <br> celldm(3) = 0.199762906, <br> nat = 2, <br> ntyp = 1, <br> ecutwfc =
25.D0 , <br> ecutrho = 300, <br> occupations = 'smearing' , <br> degauss = 0.05 , <br> smearing = 'methfessel-paxton'
<br> / <br> &ELECTRONS <br> conv_thr = 1.D-10 , <br> mixing_beta = 0.7D0 ,
<br> / <br>ATOMIC_SPECIES <br> Al 26.98000 Al.vbc.UPF <br>ATOMIC_POSITIONS angstrom <br>
Al 0.000000000 1.517315647 2.138739361 <br>Al 0.000000000 0.116702849 0.023699809 <br>K_POINTS automatic <br> 2 2 20 0 0 0 <br><br><a href="http://Al.elph.in">
Al.elph.in</a><br><br>Electron-phonon coefficients for Alwire_2 <br> &inputph <br> tr2_ph=1.0d-14, <br> prefix='al2_elph',
<br> fildvscf='al2d', <br> filelph='matrix' <br> amass(1)=26.98, <br> outdir='/root/tmp/',
<br> fildyn='al2m.dyn', <br> elph=.true., <br> trans=.true., <br> ldisp=.true.
<br> nq1=1, nq2=1, nq3=10,<br><br>And hereafter 6 modes I got<br><br> &plot nbnd= 6, nks= 27 / <br> 0.000000 0.000000 0.000000 <br> -0.0855 -0.0450
0.0000 20.7938 196.2309 372.4942 <br> 0.000000 0.000000 0.100000 <br> -13.1432 5.6657 5.7114 20.3098 196.7060 372.0899 <br> 0.000000 0.000000 0.200000
<br> -25.6753 10.2550 10.5805 18.8468 198.1533 371.0008 <br> 0.000000 0.000000 0.300000 <br> -37.6999 14.0728 14.1858 16.2544 200.5950 369.4869 <br> 0.000000
0.000000 0.400000 <br> -48.8295 11.6034 16.4265 16.4576 203.9728 367.7201 <br> 0.000000 0.000000 0.500000 <br> -58.7192 -5.6944 16.7453 17.6129 208.1190
365.6663 <br> 0.000000 0.000000 0.600000 <br> -67.0895 -15.3952 14.9673 18.4203 212.8051 363.1793 <br> 0.000000 0.000000 0.700000 <br> -73.7443 -
21.7038 11.9605 19.3942 217.8126 360.1938 <br> 0.000000 0.000000 0.800000 <br> -78.6120 -26.9948 9.8326 20.4642 222.9635 356.8134 <br> 0.000000 0.000000 0.900000
<br> -81.7857 -31.7595 10.1665 21.2176 228.1041 353.2106 <br> 0.000000 0.000000 1.000000 <br> -83.4878 -36.1149 10.5785 21.4924 233.0809 349.4591 <br>
0.000000 0.000000 1.100000 <br> -83.9637 -39.9380 6.4409 21.5912 237.7521 345.4939 <br> 0.000000 0.000000 1.200000 <br> -83.3549 -43.0700 -11.8614 21.8643
242.0400 341.2345 <br> 0.000000 0.000000 1.300000 <br> -81.7148 -45.5109 -19.5363 22.1233 245.9755 336.7214 <br> 0.000000 0.000000 1.400000 <br> -
79.2450 -47.4002 -24.2602 21.7049 249.6731 332.1110 <br> 0.000000 0.000000 1.500000 <br> -76.4698 -48.7989 -26.8527 20.1426 253.2412 327.5276 <br> 0.000000 0.000000
1.600000 <br> -74.0708 -49.5494 -28.8342 17.6459 256.7020 322.9460 <br> 0.000000 0.000000 1.700000 <br> -72.4259 -49.4368 -31.6947 14.8469 259.9856 318.2672
<br> 0.000000 0.000000 1.800000 <br> -71.2114 -48.4948 -35.6608 11.6256 263.0044 313.5063 <br> 0.000000 0.000000 1.900000 <br> -69.6799 -47.0750 -
39.7963 4.2536 265.7429 308.8670 <br> 0.000000 0.000000 2.000000 <br> -67.4586 -45.5010 -43.2503 -12.7026 268.2849 304.5960 <br> 0.000000 0.000000 2.100000
<br> -64.9647 -46.1360 -43.6300 -19.3793 270.7903 300.7406 <br> 0.000000 0.000000 2.200000 <br> -63.0506 -49.2247 -40.9136 -23.4729 273.4711 297.0578 <br> 0.000000
0.000000 2.300000 <br> -62.1609 -52.8376 -37.0315 -25.3558 276.5514 293.2015 <br> 0.000000 0.000000 2.400000 <br> -61.8563 -56.2311 -32.5370 -26.2996 280.1674
289.0264 <br> 0.000000 0.000000 2.500000 <br> -61.6387 -57.8617 -29.3445 -27.6304 283.8161 285.1565 <br> 0.000000 0.000000 2.503000 <br> -61.6384 -
57.8633 -29.3391 -27.6341 283.8284 285.1440 <br><br><br> Bac, <br><br><pre>------------------------------<br>Phung Viet Bac<br>Division of Mathematical and Physical Science,<br>Graduate School of Natural Science and Technology,
<br>Kanazawa University,<br>Kakuma, Kanazawa 920-1192, JAPAN</pre><br> <br> <br><br><br><br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br><br>your phonon branches are really strange...<br>with two atoms I would expect 6 modes per each q-point<br><br>stefano<br><br><br><br>6 branches for 2 atom are what one expects (in general 3n branches and 3<br>acoustical and 3n-3 optical ones).
<br><br>However negative values indicate some error in your calculation, dependent<br>on the magnitude and system.<br>You can impose some sum-rules for the acoustic ones, to force them to be<br>0 at the Gamma point.<br><br>
Acoustic forces are harder to calculate (smaller forces). In your case I<br>would guess up to 15 cm^1 should be ok for the acoustic ones.<br>Negative optical ones should not occur.<br><br>Best<br>Marcel Mohr<br><br><br></blockquote>
</div><br>