[Pw_forum] Inconsistencies in the CELL_PARAMETERS - ibrav=5

[Marino Vetuschi Zuccolini]

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