yambo_surf in 4.x

[tofu]

Hi,

I am new to Yambo and would like to do some surface spectroscopy on relatively large slabs, which is why I will probably need efficient memory parallelisation. As far as I understand, the parallelisation in the 4.x series has much improved, but in the changes to version 4.0.2 it says that yambo_surf has been "temporarily switched off". So would you recommend to use stable yambo_surf 3.4.2 or testing 4.0.1? Or will there be a new release with yambo_surf turned on again anytime soon?

Best,

Mat

[Conor Hogan]

Hi Mat,
Unfortunately I have not got around to porting the yambo_surf modules to the 4.x version yet. So if you really need to use things like the real space cutoff, you need to use the 3.4.2. Alternatively you can use symmetric slabs and compute by hand what spectra you need using the cell epsilons (x,y) from the 4.x versions. If you can say more about the systems you are studying and what you want to compute (RAS/SDR/HREELS) I might be able to offer some tips or workarounds. Sorry for the delays - this has slipped right down my priority list and wont be done for a few more months.
Conor

[tofu]

Dear Conor,
thanks for the quick reply! Well, I want to do RAS on symmetric slabs. Would it then be enough to calculate the cell epsilon for two perpendicular directions defined by "LongDrXp"?
Mat

[Conor Hogan]

Hi Mat,
Yes exactly - just calculate the cell epsilon for the two directions (lets say, x and y). For semiconductors the difference eps2(x-y) will already give you a good idea of the RAS at low energies, so you can use that to test convergence. You can even include higher order effects (excitons) if computationally feasible. There is no need to resort to a three-layer model with a fixed "d", just take care with factors of 2 and compute the half slab polarizability, as defined in the PRB by Manghi. If you like, you can use the simple post-processing tool ypp_surf in 3.4 to compute the RAS, using the epsx, epsy, and eps_bulk computed with the 4.x version: see the end of the RAS tutorial on Si(001)-c(4x2).
Good luck!
Conor