[QE-users] different alat values in data-file-schema.xml

[Ryky Nelson]

Hi Pietro,

thanks for the response. But how is the second alat value, within the
<output> section in data-file-schema.xml, calculated? Is it just copied
from celldm(1) and that's why the value is always the same as celldm(1)?
Ryky

On Fri, Oct 5, 2018 at 1:05 PM Pietro Delugas <pdelugas at sissa.it> wrote:

> Hello
>
> the input is generated following to the schema and  expects only lattice
> vectors in bohr units.
>
> The presence of alat and bravais_index attributes is optional and
> indicates that the cell vectors were generated with the same algorithm used
> in the latgen routine.
>
> In the case on ibrav = 0 cell vectors are arbitrarily defined by the
> user,  the routine which writes the xml file computes alat as the modulus
> of the first cell vector,  but it is probably better not to write it at all.
>
>   In the other cases you mentioned the celldm(1) provided in input was
> probably equal to the modulus of the first cell_vector.  Or celldm(1) was
> not provided at all in which case alat is computed as the modulus of the
> first cell vector.
>
> By the way in CELL PARAMETERS it is also possible to specify angstroms as
> units instead of alat and avoid to use celldm(1)
>
>
> thanks for reporting the case
>
> best regards
>
> Pietro
>
> On 05/10/2018 10:39, Ryky Nelson wrote:
>
> Hi all,
>
> some user gave me the following setup of the input file for the namelist
> SYSTEM and the card  CELL_PARAMETERS
>
>  &SYSTEM
>                        ibrav = 0,
>                    celldm(1) = 1.8897265,
>                          nat = 4,
>                         ntyp = 3,
>                      ecutwfc = 70,
>                      ecutrho = 560,
>                         nbnd = 38,
>  /
> CELL_PARAMETERS {alat}
>    3.124623266  -3.124623266   0.000000000
>   -3.124623266   0.000000000  -3.124623266
>    3.124623266   3.124623266   0.000000000
>
> After finishing the calculation with QE 6.3 with the above setup,
> strangely I got two alat values in data-file-schema.xml that are different
> from each other; the first alat value, which is put inside the section
> <input>, is 8.350483329220e0 and the other one, which is inside <output>,
> is 1.889726500000e0 [which is equal to celldm(1)]. Could any one tell me
> why they are different? My guess is that it has to do with the
> CELL_PARAMETERS setup; since it's in {alat}, the elements are supposed
> between -1 & 1, and previously, with other cases using this [-1,1] setup in
> {alat}, I always got the same alat values from the <input> & <output>
> sections? But Could any one tell me the exact reason? Thanks!
>
> Ryky
>
>
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