[Wannier] initial projections

[Zeina Al-Dolami]

Dear wannier90's owners and developers,
I have been trying to understand the examples well before going further.
One of the relevant topic that I am having hard time understanding is the
initial projections and the best way to define them for a system. I have
read the user guide and tutorials to gain more insight. Also, I have found
nice details and explanations related to the projections of carbon nano
tubes and graphene systems based on the examples provided within wannier90.
However, I am totally confused about the way that these projections are
found. My questions might be related to the chemistry, but I need your help
to start and then go from there. My questions are:

1. Prof.Nicola has mentioned that s-like projections are in the middle of
each bond that has to be identified correctly. How to identify them? To
clarify, example13 has this projection c= -2.7274, -1.9677, -0.6157 :s .
How to find these numbers for the center of projections? Is there
mathematical formula or chemistry reasons? How are they found preciously
for any system?

2. One of the pz projections of the same example is c=   3.3780, -0.7128,
-0.6157 :pz :z=  3.3780, -0.7128,  0.0000 :x=0,0,1. The center of CNT is
0,0,0.
In the forum, there is an emphasis that the direction  of the CNT along
z-axis, so z and x are identified to be along z direction. In case CNT is
along x, should we have  z=0.0,-0.7128, -0.6157 :x=1,0,0 or I am confused
by the statement in the forum??

3.In example15, one of the pz projections is
c=1.58342228,1.15042363,0.0:pz:z=0.809016993454,0.587785253559,0.0:x=0,0,1
How to get these numbers z=0.809016993454,0.587785253559,0.0? Is it same
way as question 1?

4. How or why do we choose a specific number of projections? I am assuming
it depends on the MLWF and bands that we are interested in but not sure.

You can tell from my questions that I am totally confused. Any feedback and
comments from anyone are greatly appreciated. Apologies for such long email
and questions. Looking forward to hearing from you. Many thanks in advance

-- 
Zeina Al-Dolami
PhD Candidate
Microelectronics and Photonics Graduate Program
University of Arkansas
Fayetteville, AR 72701
Office: PHYS 244
Email: zaldolam at email.uark.edu <cxm075 at email.uark.edu>
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