Dear Vito,
1) Is Yambo capable of calculating open shell periodic systems ( open shell solids ) with doublet spin state, too ?
As Daniele tod you, yambo is capable to deal with open shell solids with doublet spin states, i.e. systems with a magnetic ground-state. The main difference against non-magnetic or closed shell systems in absorption is that the BSE matrix cannot be blocked in the two spin channels, i.e. SINGLET and TRIPLETS.
In the case of magnetic systems is the code itself which diagonalize the BSE matrix in the spin space. Remember that for magnetic systems it is not possible anymore to distinguish spin eigenstate straightforwardly for a number of reasons (i.e. spin contamination, static approximation of the kernel).
2) Does Yambo produces in the output file explicitly the singlet and triplet excitation energies for, let say, closed shell periodic systems or should one read it from the data ?
For non magnetic systems yambo solves just the SINGLET block because it is the only one which has non zero oscillator strenghts and thus which contribute to the epsilon. I see Daniele gave you a solution. Other two possible solutions:
A) compute the ground state of the system with nspin=2 (collinear spin) and then use yambo if the systems were magnetic. The BSE matrix will be diagonalized in spin space and you should get exaclty the same spectrum (TRIPLET does not contribute to the epsilon) but you will see also the triplet poles inspecting the eigen-energies.
B) run a BSE calculation with "BSENGexx= 0 eV" , which should corrispond to the case of a "c only" BSE kernel. In this case pay attention that the energies will be the triplet energies (so they are ok) while the eigen-vectors and thus the shape of the epsilon will make no sense because yambo will compute the oscillator strenght assuming you are in the SINGLET block of the BSE matrix.
3) Does BSE take care of the full spin structure if the spin-orbit interaction (coupling) is of the same order of magnitude as the electron-hole interaction ?
Yes yambo can also compute the aborption spectrum including the effect of the SO interaction. In this case you just need to start from a non-collinear ground state.
2 ) There is also a small error in the devel version of yambo :
type(levels) :: E_k_p_q
Error: Object 'e_k_p_q' at (1) must have the SAVE attribute for default initialization of a component
make[1]: *** [mod_ELPH.o] Error 1
make[1]: Leaving directory `/home/vito/my_local_copy/devel/src/modules'
make: *** [yambo_ph] Error 2
I've just checked and yambo_ph in version 3.4.1 is compiling correctly. By the way:
A) are you trying to compile yambo_ph (make yamo_ph / make all) for version 3.4.1 when you get this error? (Do you need it?)
B) try to run from the directory where the yambo source is:
svn revert -R ./
make clean_all
./configure "WITH_OPTIONS_YOU_NEED"
make yambo_ph
Do you still get the error ?
C) which compiler are you using ?
Best regards,
Davide