Hi, I'm interested in calculating the Raman intensity for a material with a small indirect band overlap within LDA (~0.3 eV). As has been mentioned many times on this forum, Raman intensities cannot be calculated for a pure metal. But should I expect to be able to calculate the intensity for a material with a small, indirect band overlap? When I attempted to do so (using lraman=.true. in the ph.x calculation) I received the following messages:<br>
<br><blockquote><blockquote style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;" class="gmail_quote"> Computing Pc [DH,Drho] |psi> <br><br> Derivative coefficient: 0.001000 Threshold: 1.00E-12<br>
ik 1 ibnd 17 linter: root not converged 0.578E+08<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.763E+05<br> ik 1 ibnd 17 linter: root not converged 0.193E+11<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.119E+05<br>
ik 1 ibnd 17 linter: root not converged 0.595E+09<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.182E+05<br> ik 1 ibnd 17 linter: root not converged 0.142E+31<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.224E+24<br>
ik 1 ibnd 17 linter: root not converged 0.143E+30<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.170E+25<br> ik 1 ibnd 17 linter: root not converged 0.765E+28<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.151E+25<br>
ik 1 ibnd 17 linter: root not converged 0.643E+09<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.460E+05<br> ik 1 ibnd 17 linter: root not converged 0.619E+10<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.547E+07<br>
ik 1 ibnd 17 linter: root not converged 0.685E+09<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.810E+04<br> ik 1 ibnd 17 linter: root not converged 0.290E+34<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.848E+19<br>
ik 1 ibnd 17 linter: root not converged 0.132E+33<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.333E+18<br> ik 1 ibnd 17 linter: root not converged 0.155E+34<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.133E+20<br>
ik 1 ibnd 17 linter: root not converged 0.146E+06<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.442E+05<br> ik 1 ibnd 17 linter: root not converged 0.135E+07<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.169E+06<br>
ik 1 ibnd 17 linter: root not converged 0.567E+08<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.493E+06<br> ik 1 ibnd 17 linter: root not converged 0.292E+27<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.518E+23<br>
ik 1 ibnd 17 linter: root not converged 0.882E+28<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.215E+24<br> ik 1 ibnd 17 linter: root not converged 0.104E+29<br> kpoint 1 ibnd 17 pcgreen: root not converged 0.328E+23<br>
ik 2 ibnd 17 linter: root not converged 0.585E+21<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.363E+23<br> ik 2 ibnd 17 linter: root not converged 0.505E+21<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.119E+22<br>
ik 2 ibnd 17 linter: root not converged 0.117E+21<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.267E+22<br> ik 2 ibnd 17 linter: root not converged 0.159E+33<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.283E+27<br>
ik 2 ibnd 17 linter: root not converged 0.367E+32<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.660E+27<br> ik 2 ibnd 17 linter: root not converged 0.876E+32<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.670E+28<br>
ik 2 ibnd 17 linter: root not converged 0.249E+32<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.125E+28<br> ik 2 ibnd 17 linter: root not converged 0.348E+31<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.206E+26<br>
ik 2 ibnd 17 linter: root not converged 0.141E+30<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.561E+25<br> ik 2 ibnd 17 linter: root not converged 0.520E+36<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.990E+24<br>
ik 2 ibnd 17 linter: root not converged 0.140E+37<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.721E+24<br> ik 2 ibnd 17 linter: root not converged 0.836E+35<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.690E+25<br>
ik 2 ibnd 17 linter: root not converged 0.246E+30<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.540E+24<br> ik 2 ibnd 17 linter: root not converged 0.517E+29<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.415E+25<br>
ik 2 ibnd 17 linter: root not converged 0.133E+30<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.202E+26<br> ik 2 ibnd 17 linter: root not converged 0.570E+27<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.103E+21<br>
ik 2 ibnd 17 linter: root not converged 0.270E+29<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.451E+22<br> ik 2 ibnd 17 linter: root not converged 0.381E+29<br> kpoint 2 ibnd 17 pcgreen: root not converged 0.346E+22<br>
ik 3 ibnd 17 linter: root not converged 0.118E+34<br></blockquote></blockquote><br>and so on for each ik in the calculation. The code never crashed and I stopped it prematurely due to concern about these messages (seeing values on the order of 1E+34 is never calming). The code was also taking a very long time to calculate each ik. From what I've read in the Lazzeri and Mauri paper (PRL 90, 036401, 2003) some of the methods used to calculate the Raman tensor can take a lot of linear response calculations and so maybe I shouldn't expect it to go extremely fast. However, this root convergence worries me. The 17th band, which is the only band that this problem occurs for that I've seen, is the first conduction band of the system and is the band that indirectly overlaps with the top of the valence band. Any help or comments would be greatly appreciated!<br>
<br>Thanks,<br>Brad Malone<br>UC Berkeley<br><br>P.S. I used 'fixed' occupancies in the SCF run to avoid the 'elec. field' error in the ph.x calculation. The fixed occupancy is what I would expect for this material in experiment, as the GW bandstructure for this material predicts it to be semiconducting.<br>
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