[Pw_forum] Inconsistencies in the CELL_PARAMETERS - ibrav=5
Marino Vetuschi Zuccolini
zucco at dipteris.unige.it
Thu Dec 23 16:46:52 CET 2010
Stefano,
On 23 Dec 2010, at 16:23, Stefano de Gironcoli wrote:
> sorry but I fail to understand what you are printing ... what is your
> definition for c, tx,ty,tz ... ?
> stefano
>
right...the definition of c, tx, ty, tz are those of PW documentation
trigonal(r)
===================
for these groups, the z-axis is chosen as the 3-fold axis, but the
crystallographic vectors form a three-fold star around the z-axis,
and the primitive cell is a simple rhombohedron. The crystallographic
vectors are:
v1 = a(tx,-ty,tz), v2 = a(0,2ty,tz), v3 = a(-tx,-ty,tz).
where c=cos(alpha) is the cosine of the angle alpha between any pair
of crystallographic vectors, tc, ty, tz are defined as
tx=sqrt((1-c)/2), ty=sqrt((1-c)/6), tz=sqrt((1+2c)/3)
and here you can find the file I modified
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m.
> Marino Vetuschi Zuccolini wrote:
>> Hello to all,
>>
>> I would like to propose to your attention an apparent inconsistency in the matrix of the CELL_PARAMETERS section that I noticed during a relaxation of a crystal with trigonal symmetry (ibrav=5, in attach).
>> These inconsistency arise writing few lines in output_tau.f90 to enable the code to print the crystal parameters celldm() for each optimization step.
>>
>> This is the output of these few lines of code with a simple explanation
>>
>> ...
>> New celldm() values
>>
>> 1) celldm(1) = 10.118244326 5.354344288 # new cell edge in bohr and angstrom
>> 2) celldm(4) = 0.647279099 # cos(alpha) solved respect to c in tx
>> 3) |tx| = 0.419952914 0.419952914 # value of tx as reported in INPUT.PW and in the code
>> compared with the element of the matrix at(1,1)
>> 4) |ty| = 0.242459928 0.242459928 # value of tx as reported in INPUT.PW and in the code
>> compared with the element of the matrix at(2,1)
>> 5) |tz| = 0.874558593 >0.911266395< # value of tx as reported in INPUT.PW and in the code
>> compared with the element of the matrix at(3,1)
>> 6) c_tx = 0.647279099 # cos(alpha) solved respect to c in tx - redundant with 2)
>> 7) c_ty = 0.647279099 # cos(alpha) solved respect to c in ty
>> 8) c_tz = >0.745609664< # cos(alpha) solved respect to c in tz
>> ...
>>
>> Points 5) and 8) seem to be not consistent as expected at least by me :)
>>
>> Please, can someone explain where probably I'm going wrong?
>>
>> Many thanks to all
>>
>> m.
>>
>>
>> ------------------------------------------------------------------------
>>
>>
>>
>> *******************************************************
>> Marino Vetuschi Zuccolini
>> zucco at dipteris.unige.it
>> Researcher / Geochemist
>> Laboratory of Geochemistry
>>
>> DIPartimento per lo studio della TErra e delle sue RISorse - Universit? di Genova
>> Tel. ++39 010 3538136 Fax. ++39 010 352169
>> Corso Europa 26, 16132 - Genova - Italy
>>
>>
>>
>> ------------------------------------------------------------------------
>>
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>
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*******************************************************
Marino Vetuschi Zuccolini
zucco at dipteris.unige.it
Researcher / Geochemist
Laboratory of Geochemistry
DIPartimento per lo studio della TErra e delle sue RISorse - Universit? di Genova
Tel. ++39 010 3538136 Fax. ++39 010 352169
Corso Europa 26, 16132 - Genova - Italy
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