[Pw_forum] Calculation of Raman tensor/intensity for material with indirect band overlap
Brad Malone
brad.malone at gmail.com
Sun Nov 22 20:36:16 CET 2009
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:
Computing Pc [DH,Drho] |psi>
>
> Derivative coefficient: 0.001000 Threshold: 1.00E-12
> ik 1 ibnd 17 linter: root not converged 0.578E+08
> kpoint 1 ibnd 17 pcgreen: root not converged 0.763E+05
> ik 1 ibnd 17 linter: root not converged 0.193E+11
> kpoint 1 ibnd 17 pcgreen: root not converged 0.119E+05
> ik 1 ibnd 17 linter: root not converged 0.595E+09
> kpoint 1 ibnd 17 pcgreen: root not converged 0.182E+05
> ik 1 ibnd 17 linter: root not converged 0.142E+31
> kpoint 1 ibnd 17 pcgreen: root not converged 0.224E+24
> ik 1 ibnd 17 linter: root not converged 0.143E+30
> kpoint 1 ibnd 17 pcgreen: root not converged 0.170E+25
> ik 1 ibnd 17 linter: root not converged 0.765E+28
> kpoint 1 ibnd 17 pcgreen: root not converged 0.151E+25
> ik 1 ibnd 17 linter: root not converged 0.643E+09
> kpoint 1 ibnd 17 pcgreen: root not converged 0.460E+05
> ik 1 ibnd 17 linter: root not converged 0.619E+10
> kpoint 1 ibnd 17 pcgreen: root not converged 0.547E+07
> ik 1 ibnd 17 linter: root not converged 0.685E+09
> kpoint 1 ibnd 17 pcgreen: root not converged 0.810E+04
> ik 1 ibnd 17 linter: root not converged 0.290E+34
> kpoint 1 ibnd 17 pcgreen: root not converged 0.848E+19
> ik 1 ibnd 17 linter: root not converged 0.132E+33
> kpoint 1 ibnd 17 pcgreen: root not converged 0.333E+18
> ik 1 ibnd 17 linter: root not converged 0.155E+34
> kpoint 1 ibnd 17 pcgreen: root not converged 0.133E+20
> ik 1 ibnd 17 linter: root not converged 0.146E+06
> kpoint 1 ibnd 17 pcgreen: root not converged 0.442E+05
> ik 1 ibnd 17 linter: root not converged 0.135E+07
> kpoint 1 ibnd 17 pcgreen: root not converged 0.169E+06
> ik 1 ibnd 17 linter: root not converged 0.567E+08
> kpoint 1 ibnd 17 pcgreen: root not converged 0.493E+06
> ik 1 ibnd 17 linter: root not converged 0.292E+27
> kpoint 1 ibnd 17 pcgreen: root not converged 0.518E+23
> ik 1 ibnd 17 linter: root not converged 0.882E+28
> kpoint 1 ibnd 17 pcgreen: root not converged 0.215E+24
> ik 1 ibnd 17 linter: root not converged 0.104E+29
> kpoint 1 ibnd 17 pcgreen: root not converged 0.328E+23
> ik 2 ibnd 17 linter: root not converged 0.585E+21
> kpoint 2 ibnd 17 pcgreen: root not converged 0.363E+23
> ik 2 ibnd 17 linter: root not converged 0.505E+21
> kpoint 2 ibnd 17 pcgreen: root not converged 0.119E+22
> ik 2 ibnd 17 linter: root not converged 0.117E+21
> kpoint 2 ibnd 17 pcgreen: root not converged 0.267E+22
> ik 2 ibnd 17 linter: root not converged 0.159E+33
> kpoint 2 ibnd 17 pcgreen: root not converged 0.283E+27
> ik 2 ibnd 17 linter: root not converged 0.367E+32
> kpoint 2 ibnd 17 pcgreen: root not converged 0.660E+27
> ik 2 ibnd 17 linter: root not converged 0.876E+32
> kpoint 2 ibnd 17 pcgreen: root not converged 0.670E+28
> ik 2 ibnd 17 linter: root not converged 0.249E+32
> kpoint 2 ibnd 17 pcgreen: root not converged 0.125E+28
> ik 2 ibnd 17 linter: root not converged 0.348E+31
> kpoint 2 ibnd 17 pcgreen: root not converged 0.206E+26
> ik 2 ibnd 17 linter: root not converged 0.141E+30
> kpoint 2 ibnd 17 pcgreen: root not converged 0.561E+25
> ik 2 ibnd 17 linter: root not converged 0.520E+36
> kpoint 2 ibnd 17 pcgreen: root not converged 0.990E+24
> ik 2 ibnd 17 linter: root not converged 0.140E+37
> kpoint 2 ibnd 17 pcgreen: root not converged 0.721E+24
> ik 2 ibnd 17 linter: root not converged 0.836E+35
> kpoint 2 ibnd 17 pcgreen: root not converged 0.690E+25
> ik 2 ibnd 17 linter: root not converged 0.246E+30
> kpoint 2 ibnd 17 pcgreen: root not converged 0.540E+24
> ik 2 ibnd 17 linter: root not converged 0.517E+29
> kpoint 2 ibnd 17 pcgreen: root not converged 0.415E+25
> ik 2 ibnd 17 linter: root not converged 0.133E+30
> kpoint 2 ibnd 17 pcgreen: root not converged 0.202E+26
> ik 2 ibnd 17 linter: root not converged 0.570E+27
> kpoint 2 ibnd 17 pcgreen: root not converged 0.103E+21
> ik 2 ibnd 17 linter: root not converged 0.270E+29
> kpoint 2 ibnd 17 pcgreen: root not converged 0.451E+22
> ik 2 ibnd 17 linter: root not converged 0.381E+29
> kpoint 2 ibnd 17 pcgreen: root not converged 0.346E+22
> ik 3 ibnd 17 linter: root not converged 0.118E+34
>
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!
Thanks,
Brad Malone
UC Berkeley
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.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20091122/f8966fc2/attachment.html>
More information about the users
mailing list