[Pw_forum] graphene on BN calculation

[Davide Ceresoli]

On Wed, 16 Dec 2009, mohamed sabri majdoub wrote:

> Dear Davide,
> 
> If I change celldim(1)=1.8897261 (in Bohr radius unit), this means that the crystal lattice
> vectors are in Bohr too (same unit as alat).
Yes, the lattice vectors must be bohrradius unit.

> Crystal lattice vectors:
>     v1(1)  v1(2)  v1(3)    ... 1st lattice vector
>
>     v2(1)  v2(2)  v2(3)    ... 2nd lattice vector
>     v3(1)  v3(2)  v3(3)    ... 3rd lattice vector
> In alat units if celldm(1) was specified or in a.u. otherwise.
> Am I right? If yes then I need to change the following to Bohr units :
> 
> CELL_PARAMETERS
> 8.51980 0.00000 0.00000
> 0.00000 7.37600 0.00000
> 0.00000 0.00000 22.6120
You can change them to bohr units and set celldm(1)=1.0, or
you leave them unchanged but set celldm(1)=1.8897261.

In any case, the product CELL_PARAMETERS*celldm(1) must always
match your wanted lattice spacings in bohr units, not in angstrom.

This is in contrast with ATOMIC_POSITIONS, where one can choose
to enter them in angstrom/bohr/alat/crystal units.

HTH.

Davide