[Wannier] Initial choice for projection

[Nicholas E. Singh-Miller]

Dear Seunghwan,

The case of the CNT is a bit trickier (that other cases) to wannierize to 
the correct final configuration.

>
> Begin Projections
> Random
> C:pz:x=0,0,1
> End Projections
>
> It went through without a problem although the final results (band
> structure, DOS) were somewhat different from the example.

Because the example case is well tested and carefully set up, this
is a good indication that the final Wannier functions are probably not 
what you want.

>
> The trial orbitals for disentanglement are not orthonormal
> Exiting.......
> Error in dis_main: orthonormal error 1
>
> I even tried the same projection like the one in example for 4 unit cells,
> but it didn't work neither with the same error message.

You may want to include your .win file so others can see the exact set up.

> [3] What is the best option for initial projection in carbon nanotube
> system?

It seems the best option for CNTs is the way they are set up in the 
example.  That is place "s" states on the bond centers and "p_z" states on 
each carbon.  The key is to have the p_z point out of the CNT. for 
instance (from the example):
c=   3.3780, -0.7128, -0.6157 :pz :z=  3.3780, -0.7128,  0.0000 :x=0,0,1

this is saying that a center (in cartesian coords) 3.3780, -0.7128, 
-0.6157 should have a pz projection.  the z= and x= are the axis for this 
orital (which will lie along z).  so for this case, because the CNT is 
longitudinally along the z-axis, we have to reset the x=0,0,1 and the z 
is pointing out from the center of the CNT (which you could acomplish by 
using the orientation (x-x0,y-y0,0) where x0,y0 is the center of the CNT, 
in this case that is 0,0 so the coords are the same as the wannier 
center).

Where as in your previous test C:pz:x=0,0,1
the z-axis is not redefined (and would be the default z=0,0,1 ... which 
may be the cause of your orthonormality problems).

In general, I think that the CNT is a tricker problem than some of the 
others (e.g. there are times for other systems where choosing a random 
starting projection could work).

regards,

Nick


*****************************************
Nicholas E. Singh-Miller
Prof. Marzari Group (quasiamore.mit.edu)
Materials Science and Engineering
Massachusetts Institute of Technology
13-4066
(617)324-0372
*****************************************