Hi, I'm Leonardo M M Jorge, the one who put the LDA-1/2 method on QE. And yes, it is working!
You indeed have to create a new pseudopotential with ld1.x and the flag "iswitch=4" (among other options, shown in the example file atomic_doc/pseudo-LDA-0.5/si.lda.0.5.in ), and then use it on a standard LDA calculation. You obtained results very similar to standard LDA because one of these other options is not well set. When generating the pseudo, besides the electronic configuration used (of a half-ionized atom, hence the name -0.5 ), there is also another parameter needed: rcutv, which is the radius where you cut the perturbation. The value set on the example file (1.0) is too small; for Silicon these values should be somewhere around 3.6. To obtain the right value for this rcutv parameter you need to do several calculations, changing it by small steps, and then get the rcutv where the gap of the system is an extremum (maximum or minimum). The explanation why this works is written on the reference you just cited ( L. G. Ferreira, M. Marques and L. K. Teles, Phys. Rev. B 78 125116 (2008) ), but what's important is that it IS NOT a free parameter (one you keep changing until you get the result you want), as there is a procedure to obtain it. Also, as small variations of the rcutv parameters should give very small variations of the Electronic Gap (as it is an extremum for variations), we assume that you can obtain the right rcutv value for a small and simple system, and then use it on a bigger and more complex system (for a given atom; different atom kinds have different rcutv!). I hope I could explain the method for you, if you have any more questions feel free to write me. Leonardo Jorge PhD Student Universidade de S?o Paulo - Brazil