Hii users,

I have one general question. In the optic utility https://docs.abinit.org/guide/optic/, somewhere written here is **RPA**, and sometimes it is written that “**Note that optic works in the independent-particle approximation (IPA)**” . Then why is the RPA term written here in this tutorial? Because sometimes this gives the information that optic utility is based on the RPA. I think this could be a little confusing. Please let me know if I have a misunderstanding here.

Dear Vinod Solet,

You are right, the simultaneous usage of RPA and IPA acronyms in this tutorial is confusing. Moreover, it is rooted in the litterature. Anyhow, referring to what is done in Optic as “Independent Particle Approximation”, and getting rid of “RPA” in this context is the safest. So, it has been fixed, and will appear in the next v9.10 in about one month or so …

Best,

X

Hello Dr. Gonze,

Thank you for your clarification. Actually, I have read the “Draxl2006” paper, where they have used bare one-particle propagator G^0 in the RPA dielectric function (**Lindhard formula**) for calculating the polarizability P, which means up to Hartree level. We can also call this procedure by ‘IPA’, because electron-hole interaction is not considered here. So may be, RPA and IPA are the same in the Optic, because Optic also does not include the electron-hole interaction. **Can we understand this as “RPA at DFT level”?**

Please rewrite here if I am interpreting it wrongly.