Dear Wien2k mailing list, I'm trying to calculate a band structure of Tb3Ga5O12 magneto-optical crystal (cubic Ia-3d, 80 atoms). While I consider myself quite experienced Wien2k user, I've always managed to stay away from f block elements, so my experience here is none. So besides the few questions I have I'll also try to somehow summarize what I did, please correct me if something was not OK.
Luckily I'm not shooting completely blind as I have some high-quality optical data where we can see some (very weak but also quite sharp and hence noticeable f-f transitions in the band gap so I have some idea how the Tb f states at least should look like). Significant optical absorption start around 4eV but below that I see some very weak electronic transitions in the 0.2-0.9eV range, around 2.5 and 3.5eV (reportedly between f states located in the band gap). So I expect at least three bunches of f states in band gap one occupied and the others unoccupied. I've started with spin-polarized PBE, I'm reasonably sure the structure file is OK, albeit probably not much relaxed (but I was hoping I could find equilibrium volume and do relaxation at a later point). I did not opt for HDLOs even though the Tb sphere is quite big (2.43) since I would also like to try to get few momentum matrix elements later with optics, but I've increased the lmax to 14 and lvnsmax to 8 (lapw2 GMAX 16, fft factor 3 and 4x4x4 k-grid). The initial runsp went fine but the band structure is far from OK, I get only a single bunch of f states in the band gap clumped together (some of them are occupied so its metallic), but experimentally I should get and insulator (although the difference between the unoccupied and occupied f states in the band gap is only maybe 0.2eV). Regarding the f electron correction I opted for onsite hybrid and initialized it with init_orb_lapw -eece. UG says that its better to use LDA for the exchange potential so I copied case.in0 to case.in0eece_lapw where I replaced "XC_PBE" on the first line with "EX_PBE VX_LDA EC_PBE VC_PBE". The onsite hybrid calculation converged fine, I get a nice splitting of the f states (albeit a bit too much maybe). The other options would be +U obviously, I went for the hybrid because it felt more rigorous, but I would also appreciate comments if someone has maybe better experience with +U? Next step was to initialize spin-orbit interaction with init_so_lapw. I started with the default 001 but I want to also try other directions later and compare. I opted for no relativistic LOs (no support in optics) and enabled it only for Tb and Ga. symetso created a new structure (most notable I have more Tb inequivalent positions) and than I manually fixed case.inso case.indm and case.inorb as the init_so script warned me. I also guessed I should fix case.ineece (that seemed straightforward) but than I thought I should also fix case.in2eece. Reading UG gives the impression that case.in2eece is normal case.in2 with extra EECE on the first line and than the optional 3a and 3b lines. In the case.in2eece created automatically with init_orb_lapw - eece the 3a and 3b lines looked like: 1 1 1 3 However reading UG this actually seems wrong? Because UG says (Section 7.9 page 166) the format for optional 3b is just two values: jatom rho, l rho so I wonder if the UG is wrong or if I'm actually applying the hybrid correction to p instead of f? Also, is there anything else I should fix manually after intializing the so on top of eece? Or should I do it the other way around (first so and then eece)? The reasoning for doing first eece was that I get a metal with plain PBE and an insulator with the onsite hybrid, so I thought it might be easier to converge if I start so from insulator (but I still use TEMP smearing just to be sure I don't end with convergence problems if I get a metal during the convergence as the expected unoccupied occupied f-f distance is very small.) I was also considering mBJ later, just to get some feeling how the conduction bad would shift but I'm not sure if this would work or not on top of eece and so? One last question is regarding the forces. From reading the UG I understood that it should be OK to relax the oxygen positions with onsite hybrid and so (as long as I don't have so or eece enabled for O atoms). Is this correct? So will just switching to MSR1a and running normal runsp -so -eece work or are some other fixes needed? Best regards Pavel _______________________________________________ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
