[Pw_forum] about alat in atomic-position

[Katalin Gaal-Nagy]

> Dear All,
>
>   Which is the difference between the "alat'' (the unit of alat)  and
> "angstrom" in the ATOMIC_POSITIONS card.
>

You can give the atomic positions in units of the lattice constant (alat),
meaning in relative units.

For example: Si has in the fcc lattice the basis atoms at
(000) and (0.25,0.25,0.25) in "alat" or at (000) and
(1.357,1.357,1.357) in Angstrom (if the lattice constant is 5.43 Angstron.

If you are using the unit alat for non-cubic systems, you have to scale
the y- and z-coordinate with b/a or c/a respectively (since the unit is
alat=a)

Best wishes,
Katalin