Strange behaviour with spin, but only in supercell
Posted: Tue Aug 21, 2018 1:14 pm
Dear Yambo community,
since I am currently working on a rather large system (polaron at a point defect in a lithium niobate supercell with 80 atoms), I started by calculating the linear response for two test systems, both without point defects and polarons (stoichiometric): The primitive cell with 10 atoms and without spin (system "1" in my notation), and the 2x2x2 repetition with 80 atoms with spin ("29"). Additionally, I used two waypoints: A 10 atom cell with spin ("3") and an 80 atom cell without spin ("18").
Please have a look at the attached figure (plot.pdf): "Switching on" the spin in the small cell ("1"->"3") does not change the result noticeably, as expected. Neither does changing to the supercell ("1"->"18"). Technically, there are changes, but those had to be expected, since I used less k-points. The strange behaviour occurs, when we try to calculate the supercell including spin: The linear response is way too large (factor 4) and its form does not fit too well, either.
Im am not certain how to explain this, since the energies in chapter 02.05 of the file r-IPA_optics_chi are very similar for systems "18" and "29".
Attached you will find all files I used for my calculations. I would be grateful for any suggestions.
Best,
Falko
since I am currently working on a rather large system (polaron at a point defect in a lithium niobate supercell with 80 atoms), I started by calculating the linear response for two test systems, both without point defects and polarons (stoichiometric): The primitive cell with 10 atoms and without spin (system "1" in my notation), and the 2x2x2 repetition with 80 atoms with spin ("29"). Additionally, I used two waypoints: A 10 atom cell with spin ("3") and an 80 atom cell without spin ("18").
Please have a look at the attached figure (plot.pdf): "Switching on" the spin in the small cell ("1"->"3") does not change the result noticeably, as expected. Neither does changing to the supercell ("1"->"18"). Technically, there are changes, but those had to be expected, since I used less k-points. The strange behaviour occurs, when we try to calculate the supercell including spin: The linear response is way too large (factor 4) and its form does not fit too well, either.
Im am not certain how to explain this, since the energies in chapter 02.05 of the file r-IPA_optics_chi are very similar for systems "18" and "29".
Attached you will find all files I used for my calculations. I would be grateful for any suggestions.
Best,
Falko