<div>Dear Users, </div>
<div>I am willing to run electron-phonon calculations for my Ni system of interest and have few queries to clarify and questions as well. I will highly appreciate your answers towards better understanding of the el-ph calculations. </div>
<div> </div>
<div>Based on Al example, I have gathered that after scf-relaxation (for dense k points), the el-ph calculations is performed this way. </div>
<div>1. Estimate # of q points (based on provided nqs)</div>
<div>2. For each q point, calculate the dynamical matrix</div>
<div> 2a) First estimate # of irreducible representations (which are the branches in phonon dispersion curve) for that q</div>
<div> 2b) For each irreducible representation, run the convergence test</div>
<div>3. Once 2a) and 2b) are done, diagonalize the dynamical matrix. </div>
<div>4. Calculate the frequencies (n) for that q. </div>
<div>5. Calculate lambda (q,n) and gamma (q,n) with 10 different gaussian broadening (0.005 to 0.05)</div>
<div>6. Proceed to step 2 for next q. </div>
<div> </div>
<div>Please guide if my understanding is wrong. The queries I have are follows</div>
<div> </div>
<div><strong>A. What is gamma (q,n) in point 5 which shows in elph output file as follows. </strong></div>
<div> lambda( 2)= 0.0841 gamma= 72.85 GHz<br> lambda( 3)= 0.0306 gamma= 97.74 GHz<br><strong></strong></div>
<div><strong>B. The lambda and gamma are calculated for 10 different gaussian broadening values. This value is irrespective of what is used in scf.fit calculations prior to elph calculations. How should we interpret these 10 values? How should one decide which gaussian broadening is appropriate? </strong></div>
<div> </div>
<div>Now coming to my problem of interest. I am planning to calculate cummulative lambda for single layer of Ni atoms. So, I start by relaxing a bulk Ni crystal, cut out a fcc plane from (relaxed crystal) that with 4 atoms and create a supercell (with empty vaccum space). Now, I run scf calculation with dense grid (24,24,8) followed by second scf run with (8,8,2) grid. Then I run my elph-calculation. Here is the input file for elph. </div>
<div> </div>
<div> &INPUTPH<br> outdir = './' ,<br> prefix = '1slab' ,<br> fildyn = '1slab.dyn' ,<br> fildvscf = '1slab' ,<br>
ldisp = .true.,<br> tr2_ph=1.0d-10,<br> nq1 = 8 ,<br> nq2 = 8 ,<br> nq3 = 2 ,<br> alpha_mix(1) = 0.4 ,<br>
epsil = .false.,<br> elph = .true.,<br> fpol = .false. ,<br> recover = .false. ,<br> amass(1) = 58.69340 ,<br> iverbosity = 1 ,<br>
/<br></div>
<div><strong>I have two more questions for this particular system. </strong></div>
<div><strong>1. For q=(0,0,0) convergence is achieved successfully. However, I see 2 negative frequencies. Similarly for q=(0,0,-0.12), I see one neg frequency. Does that mean that</strong></div>
<div><strong> a) My atoms are not fully relaxed. </strong></div>
<div><strong> b) My SCF grid is not dense enough?</strong></div>
<div><strong> c) erho, ecut values are not big enough? I used erhowfc of 55 and erhocut of 550?</strong></div>
<div><strong></strong> </div>
<div><strong>Please guide.</strong></div>
<div><strong></strong> </div>
<div><strong>2. For the next q point, I do not get convergence acheived in 100 (default) interations for certain polarization. This is what I get at the end</strong></div>
<div><strong></strong> </div>
<div> iter # 89 total cpu time : 8505.8 secs <a href="http://av.it">av.it</a>.: 34.3<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.439E+23</div>
<div> iter # 90 total cpu time : 8648.0 secs <a href="http://av.it">av.it</a>.: 36.0<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.592E+23</div>
<div> iter # 91 total cpu time : 8790.0 secs <a href="http://av.it">av.it</a>.: 35.9<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.195E+25</div>
<div> iter # 92 total cpu time : 8931.3 secs <a href="http://av.it">av.it</a>.: 35.7<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.199E+25</div>
<div> iter # 93 total cpu time : 9079.5 secs <a href="http://av.it">av.it</a>.: 37.7<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.197E+25</div>
<div> iter # 94 total cpu time : 9230.5 secs <a href="http://av.it">av.it</a>.: 38.4<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.295E+27</div>
<div> iter # 95 total cpu time : 9382.6 secs <a href="http://av.it">av.it</a>.: 38.7<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.426E+26</div>
<div> iter # 96 total cpu time : 9538.3 secs <a href="http://av.it">av.it</a>.: 39.8<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.130E+27</div>
<div> iter # 97 total cpu time : 9697.1 secs <a href="http://av.it">av.it</a>.: 40.4<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.182E+29</div>
<div> iter # 98 total cpu time : 9855.5 secs <a href="http://av.it">av.it</a>.: 40.4<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.216E+28</div>
<div> iter # 99 total cpu time : 10019.0 secs <a href="http://av.it">av.it</a>.: 41.8<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.732E+28</div>
<div> iter # 100 total cpu time : 10183.3 secs <a href="http://av.it">av.it</a>.: 42.0<br> thresh= 0.100E-01 alpha_mix = 0.400 |ddv_scf|^2 = 0.123E+31</div>
<div> End of self-consistent calculation</div>
<div> No convergence has been achieved<br></div>
<div> </div>
<div><strong>It can be seen that |ddv_scf|^2 is exponentially increasing instead of decreasing. What could be the possible reason behind it? </strong></div>
<div> </div>
<div>Any help will be highly appreaciated. </div>
<div>Thanks in advance and best Regards,</div>
<div>Vikas</div>
<div> </div>
<div>Computational Reasearcher, </div>
<div>Wright Patterson Air Force Base, Dayton OH.</div>