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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