[Pw_forum] newbie question: K-points, funtional choise and PP generation/use

[Пермяков Евгений]

Hi! I'd like to use quantum espresso in research of properties of MoS2 
nanoparticles, modified with Co and Ni. This basically means 
calculations with 20 to 60 atoms of modified MoS2 slab and 10 to 30 
atoms of interacting molecule, as well as 1- and 3-dimensional periodic 
calculations with same number of atoms. The atomic species of interest 
are: Mo, S, Co, Ni, H, C, N, O, K, Na, Li.

Before performing real calculations I'd like to reproduce geometry of 
several basic with reasonable agreement with expreimental data. The 
problem is choise of PP/functional pair. For some time I was stick with 
b3lyp and pbe functionals of gaussian-03 package with full-electron 
non-periodic calculations, wich resulted in good agreement with 
experimental data. However, I cannot find PPs for this functionals for 
QE and full-electron approach is a little too much for my new systems. 
With quick research I was able to generate simple PP for H atom, but 
got  0.78  A H-H bond length instead of 0.74, and runned into 
incompatibility of ultrasoft PP and Gamma algorithm.  So, I decided to 
stop and search for advise.

The questions are:

 1. Can someone point a good review about PP approximation (both math
    and use)?
 2. As well as planewave approach for basis sets (It is completly new
    for me, I used only GTO basis sets before) ?
 3. And possibly a good library of PP (espetially interested in
    desription of generation procedure) ?
 4. What the hell are K-points, given in K_points sections and how
    should I choose them for ultrasoft PP ?
 5. Are geometry and energy errors in QE/DFT systematic, i.e. can I use
    some corrections coefficient or I should work with them as random
    values?

Of course, I'm going at least to try to find and read reference articles 
for QE, yet my math skills are not very hight.

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