if you are interested in comparing with the definition of in INPUT.PW you should apply the definition in INPUT.PW... which is not the one you are using. There is a value of "a" missing in your definition.
stefano Marino Vetuschi Zuccolini wrote: > stefano, > thanks but can you explain a little bit more exhaustively, because I do not > understand. It seems that tx and ty and the cos(alpha) derived from them are > numerically exact and I suppose the algorithm are right. > > ... > v_1=sqrt(at(1,1)**2+at(2,1)**2+at(3,1)**2) > cell_edge=alat*v_1 > c_tx=(1-2*(at(1,1))**2) > c_ty=(-6*at(2,1)**2)+1 > c_tz=((3*at(3,1)**2-1)/(2)) > .... > > tx=sqrt((1-c)/2) > ty=sqrt((1-c)/6) > tz=sqrt((1+2*c)/3) > ... > > m. > > > On 23 Dec 2010, at 17:28, Stefano de Gironcoli wrote: > > >> Dear Marino Vetuschi Zuccolini wrote: >> >>> 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) >>> >>> >> in order to extract c you are forgetting to divide v1 by a=|v1|. >> >> stefano >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://www.democritos.it/mailman/listinfo/pw_forum >> > > > > ******************************************************* > 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 > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >
