[Pw_forum] cartesian (angstrom) to alat units

[Ari P Seitsonen]

Hello,

   In order to clarify: There are several ways to specify the coordinates 
to PWSCF/QE:

  - In Ångström
  - In Bohr
  - In units of lattice constant, 'celldm(1)' in Bohr or 'a' in Ångström
  - In units of lattice vectors

   This you can choose on the line containing 'ATOMIC_POSITIONS'. Like 
noted above, one can use 'celldm(1:6)', alternatively 'a', 'b' and 'c' 
(plus 'cosab', 'cosac', 'cosbc') if you want to use Ångströms instead. 
Please have a look in the documentation, in particular 'INPUT_PW.*', below 
the section 'ibrav'. One more to specify the cell vectors is 'ibrav = 0' 
and the section 'CELL_PARAMETERS'.

   Hopefully this helps.

     Greetings,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari P Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   Physikalisch-Chemisches Institut der Universitaet Zuerich
   Tel: +41 44 63 54 497  /  Mobile: +41 79 71 90 935


On Thu, 25 Oct 2012, Gisela Bocan wrote:

> Hi,
>      If I am not mistaken, every coordinate should be in celldm(1) units. celldm(1) should be in bohr, so, if you have a coordinate X in Ang you should write X_bohr/celldm(1) (where X_bohr
> is X converted to bohr).
> 
> Hope it helps!
> Bye!
> Gisela.
> 
> On Thu, Oct 25, 2012 at 4:09 PM, Bodiford, Nelli K <nelli.bodiford at mavs.uta.edu> wrote:
>       Celldm should be in Bohr, that's what I have been using and it works. Hope it helps!
> 
> On Oct 25, 2012, at 1:54 PM, David Furman wrote:
>
>       Dear Espresso fans,
>  
> I would like to make a series of calculations in different lattice parameter values.
> If I understand correctly, the atomic positions should be in units of the lattice parameter "a" (default) in order for them to stay the same for every lattice parameter.
> So, I assume each Cartesian coordinate in Ang should be a fraction of lattice parameter: X/a
> But, does the lattice parameter should be in bohr (like in celldm(1)) or in Ang as well ?
>  
> Thank you
>  
>  
>  
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