[CPMD-list] Explanation for SYSTEM section

[Ari.P.Seitsonen at iki.fi]

Dear Mahesh,

> &SYSTEM 
>    POINT GROUP 
>     AUTO 
>    SYMMETRY 
>     4 
>    CELL 
>     2.802    1.0    5.7155     1.0  1.0  1.0    (alat=3.962,
> c/a=7*sqrt(2/3)) 
>    CUTOFF 
>     40.000 
>    ANGSTROMS 
>    STATES 
>     22 
>    SCALE 
>    TESR 
>      3 
>    KPOINTS MONKHORST-PACK FULL 
>     7 7 1 
>  &END
> 
> The  above input was from one of the examples given in Prof. Hutter's
> homepage. The input says, the system is hexagonal (since SYMMETRY = 4).
> For hexagonal, a = b $B!b(J c and Alpha = Beta= 90 and Gama = 120.
> But in this example, it is taken as COS (Alpha) = 1.0, which means
> Alpha = 0. 
> 
> Could anyone explain to me this?.. Also I would appreciate if some of you
> can explain to me how the unit cell is repeated in this case.

Please check 'latgen.F': The values CELLDM(4:6) are not used because
in the hexagonal cell all the angles are already defined, like you
write. So actually those values are redundant, and their values not
used.

    Yours,

       apsi

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