third-order corrected Hessian matrix

[anyi-mxh]

Dear Developer,

Hello, in the LaH10 and H3S examples, were only second-order corrected Hessian matrices considered? What parameters are needed for the third-order corrected Hessian matrix, and are there any examples available for reference?

Thank you very much for your time and support. I look forward to your response.

Best regards,
mxh

[mesonepigreco]

Dear mxh,
I assume you are referring to the Tutorials directory of the repositories.
Those are very underconverged results to run quickly as examples. The free energy Hessian for the H3S is computed with the bubble approximation, which always accounts for third-order but not for fourth-order (i.e., it neglects 4-phonon scattering in the self-energy, but still the effect of 4-phonon scattering is accounted by the standard SSCHA relaxation with the "loop" diagram).

H3S and LaH10 calculations are reported in the two papers:
H3S: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.214101
LaH10: https://www.nature.com/articles/s41586-020-1955-z

where you find converged results for the free-energy Hessian as a function of the number of configurations and the supercell size.