ABINIT Discussion Forums

hello
I have the phonon frequencies for LaCoO3 but I don't know which of them are LO and TO?

Phonon frequencies in cm-1 :
- 4.823958E+01 4.823958E+01 4.964588E+01 2.410723E+02 2.410723E+02
- 2.420758E+02 2.576340E+02 2.576370E+02 2.576370E+02 4.151637E+02
- 4.167719E+02 4.167719E+02 5.579571E+02 5.579571E+02 5.585992E+02

thanks

Hello,

1) if this is for gamma, you have quite a large acoustic sum rule break. You should run anaddb with asr 1 or 2, and check your pseudopotential and ecut convergence.

2) you should start with the theory, e.g. read chap 27 of Ashcroft and Mermin. The LO mode is the non-degenerate, higher frequency mode.

3) to calculate the LO-TO splitting, follow the response function tutorials for AlAs carefully, and use qph2l / nph2l in anaddb


Matthieu