[Wien] charge density in CLM files

[Peter Blaha]

1) I hope you agree: the electron density (psi^* psi) must be a "real"
function.
The usual definition of spherical harmonics gives them as a complex
function. However, one can always form some linear combination and
obtain "real"-spherical harmonics. This is what is used here. More
specifically, we use "lattice" harmonics, i.e. a symmetry adapted
selection of some spherical harmonics.

2) This "syntax" is connected with the selection of "lattice harmonics".
Of course a "negative"-l does not mean that l is negative, but indicates
a particular form of linear combination. For more details see the UG or
the original papers (cited in the UG).

>      1) why the density in MT sphere given in case.clmXX files are all 
> real values
>         rather than complex values for all radial points. Based on the 
> userguide, these values
>         represent the coefficients of spherical harmonic 
> expansion,according to this,
>         these coefficients should be complex values not real ones. so ,I 
> want to know
>         what the so-called "density" for MT sphere in clm file really 
> mean !!
>  
>      2) occasionaly,some of the lattice harmonic indexes for L listed in 
> case.in2 are negative,
>         and the possible LM listed in the table in the LAPW2 chapter in 
> userguide  
>         also indicate that L can  negative,furthermore, I read the 
> related source codes
>         and find that some   programs are firmly connected with this 
> issue. thus, I am puzzled about  this,because L should not be negative (>=0)
>        
>       I am eager to figure out what is going on about the two issues, 
> can you give me some ideas
>  or let me know the details of both of them.
>  
> thanks very much  !
>  
> Ming Wenmei
> 
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