Dear all,

We have done some calculations using the option:

  WriteMullikenPop       3

I would like to know what is precisely the meaning of the off-diagonal terms 
that are printed in the output (see example with relevant input and output 
below). 

I understand that the diagonal terms give the Mulliken charges on the atoms 
from the diagonal terms of the rho*S, where rho = density matrix and S is 
the overlap of basis orbitals. If that is not correct, I would appreciate if 
somebody could enlighten me.

But how about the off-diagonal? I considered the possibility that they would 
give the off-diagonal terms of the rho(k)*S(k) matrix, i.e., in the basis of 
Bloch sums, but they are not printed per k-point, so this does not seem 
right. 

To put it another way, since atom i and j can be neighbors more than once, 
considering the periodic images, what would the off-diagonal terms in the 
matrix below represent?

Thanks a lot in advance for any help on this.

Ricardo Nunes
Departamento de Fisica - UFMG


================
Input:
================
WriteMullikenPop       3
# Species and atoms
NumberOfSpecies        1
NumberOfAtoms          2
%block ChemicalSpeciesLabel
  1  79  Au
%endblock ChemicalSpeciesLabel

LatticeConstant     2.673694  Ang
%block LatticeVectors
    9.350359    0.000000    0.000000
    0.000000    9.350359    0.000000
    0.000000    0.000000    1.000000
%endblock LatticeVectors

# Atomic coordinates
AtomicCoordinatesFormat     Ang
%block AtomicCoordinatesAndAtomicSpecies
    0.04618072    0.04352611   -0.00000014   1  Au        1
    0.04608645    2.47934396    1.33684744   1  Au        2
%endblock AtomicCoordinatesAndAtomicSpecies

================
Output:
================
mulliken: Overlap Populations between Atoms

                 1       2
           1  10.488   0.100
           2   0.100  10.489

mulliken: Overlap Populations between Orbitals

                   1        2        3        4        5        6        7      
  
8
                  6s       6s       5dxy     5dyz     5dz2     5dxz     
5dx2-y2  5dxy
   1 6s          0.780   -0.018    0.000    0.000    0.000    0.000    0.000    
0.000
   2 6s         -0.018    0.138    0.000    0.000    0.000    0.000    0.000    
0.000
   3 5dxy        0.000    0.000    1.954    0.000    0.000    0.000    0.000    
0.008
   4 5dyz        0.000    0.000    0.000    1.853    0.000    0.000    0.000    
0.000
   5 5dz2        0.000    0.000    0.000    0.000    1.795    0.000    0.000    
0.000
   6 5dxz        0.000    0.000    0.000    0.000    0.000    1.923    0.000    
0.000
   7 5dx2-y2     0.000    0.000    0.000    0.000    0.000    0.000    1.898    
0.000
   8 5dxy        0.000    0.000    0.008    0.000    0.000    0.000    0.000    
0.003
   9 5dyz        0.000    0.000    0.000    0.014    0.000    0.000    0.000    
0.000
  10 5dz2        0.000    0.000    0.000    0.000    0.001    0.000    0.000    
0.000
  11 5dxz        0.000    0.000    0.000    0.000    0.000    0.010    0.000    
0.000
  12 5dx2-y2     0.000    0.000    0.000    0.000    0.000    0.000    0.014    
0.000
  13 6Ppy        0.000    0.000    0.000    0.000    0.000    0.000    0.000    
0.000
  14 6Ppz        0.000    0.000    0.000    0.000    0.000    0.000    0.000    
0.000
  15 6Ppx        0.000    0.000    0.000    0.000    0.000    0.000    0.000    
0.000
  16 6s         -0.024    0.012    0.000    0.003    0.000    0.000    0.000    
0.000
  17 6s          0.012    0.008    0.000    0.003    0.000    0.000    0.004    
0.000
  18 5dxy        0.000    0.000    0.001    0.000    0.000    0.000    0.000    
0.000
  19 5dyz        0.003    0.003    0.000   -0.002   -0.001    0.000   -0.002    
0.000
  20 5dz2        0.000    0.000    0.000   -0.001   -0.001    0.000    0.000    
0.000
  21 5dxz        0.000    0.000    0.000    0.000    0.000    0.000    0.000    
0.000
  22 5dx2-y2     0.000    0.004    0.000   -0.002    0.000    0.000    0.000    
0.000
  23 5dxy        0.000    0.000    0.000    0.000    0.000    0.000    0.000    
0.000
  24 5dyz        0.000    0.000    0.000    0.000    0.000    0.000    0.000    
0.000
  25 5dz2        0.000    0.000    0.000    0.000    0.000    0.000    0.000    
0.000
  26 5dxz        0.000    0.000    0.000    0.000    0.000    0.000    0.000    
0.000
  27 5dx2-y2     0.000    0.000    0.000    0.000    0.000    0.000    0.000    
0.000
  28 6Ppy        0.007    0.005    0.000    0.008    0.000    0.000    0.003    
0.000
  29 6Ppz        0.005    0.002    0.000    0.000    0.002    0.000    0.004    
0.000
  30 6Ppx        0.000    0.000    0.005    0.000    0.000    0.001    0.000    
0.000

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