[Pw_forum] about the convergence of ph.x

[sun jason]

dear all,

I will very appreciate the one who help me about following question,

the ph.x is not convergence when I calculate the second order response.

the message is like this:
     Computing Second order response 
     kpoint   4 ibnd  41 pcgreen: root not converged 0.274E+01
     kpoint   4 ibnd  41 pcgreen: root not converged 0.424E+04
     kpoint   4 ibnd  41 pcgreen: root not converged 0.479E+02
     kpoint   4 ibnd  41 pcgreen: root not converged 0.162E+07
  
      iter #   1   av.it.:  50.3
      thresh= 0.100E-01 alpha_mix =  0.700 |ddv_scf|^2 =  0.472E+28
     kpoint   4 ibnd  41 pcgreen: root not converged 0.819E+01
     kpoint   4 ibnd  41 pcgreen: root not converged 0.160E-01
     kpoint   4 ibnd  41 pcgreen: root not converged 0.167E+00

      iter #   2   av.it.:  54.0
      thresh= 0.100E-01 alpha_mix =  0.700 |ddv_scf|^2 =  0.653E+30
     kpoint   4 ibnd  41 pcgreen: root not converged 0.214E+04
     kpoint   4 ibnd  41 pcgreen: root not converged 0.151E+02
     kpoint   4 ibnd  41 pcgreen: root not converged 0.740E+03
......

I've change the mixing_beta to 0.1, but the situation is not change to 
better.
should I change the nbnd ? the default nbnd=40.
does this message mean the number of bands is not enough ?
 
Thank you in advance!

Best regards,
===============================================
Jian SUN 
Physics Dept. of Nanjing University 
National Lab. of Solid State Microstructures 
22 Hankou Road, Gulou District 
Nanjing, Jiangsu Province 
210093 
China 
===============================================