[Pw_forum] force constants file

[Bartek Wiendlocha]

Hello,

Could Anyone help me and write a (detailed..) description of the force
constants file, generated with q2r (usually *.fc)?
for ex.: (metallic system)
------------
  2    3  4  5.6370000  0.0000000  1.0870000  0.0000000  0.0000000
0.0000000 --> lattice

           1  'Al '  -> atoms  24588.6885119930 -> ??
           2  'B  '  -> atoms  9851.88001536857 -> ??
    1    1      0.0000000      0.0000000      0.0000000 -> positions
    2    2      0.5000000      0.2886751      0.5435000
    3    2      0.0000000      0.5773503      0.5435000

 F
   8   8   8  -> grid size
   1   1   1   1  --> ??
   1   1   1  --> ?? 1.56778730300E-01 --> force constant, but for which
atoms?
   2   1   1  -2.70214755142E-02
.....etc...
-----------------

are the force constants divided by mass ? How to find the distance in
real space (or the number of nearest neighbours) up to which the FC are
calculated?
I need these information to calculate the inverse force constant matrix
(I think so..).

Thanks for help,
Bartek


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