Dear all, I think that (using GAO Zhe's notation) both b (*) c / (|b| |c|) and a (*) b / (|a| |b|) should give the same result, because in the rhombohedral lattice the three basis vectors form equal angles with each other. Obviously, a (*) b / (|a (*) b|) is not correct because it would always give 1 or -1 (and I believe it was just a typo).
HTH GS On 11/17/2011 06:49 AM, Huiqun Zhou wrote: > I'm afraid the formula for calculating cosA should be > cosA = b (*) c / (|b| | c|) > dr. zhou huiqun > @earth sciences, nanjing university, china > > ----- Original Message ----- > *From:* GAO Zhe <mailto:flux_ray12 at 163.com> > *To:* PWSCF Forum <mailto:pw_forum at pwscf.org> > *Sent:* Wednesday, November 16, 2011 8:53 PM > *Subject:* Re: [Pw_forum] calculation of lattice parameter and > angle of rhombohedral structure > > the three basis vectors of rhombohedral are (after relaxation) : > a = ( 0.636439417 -0.367448469 0.640642896 ) > b = ( 0.000000000 0.734896938 0.640642896 ) > c = ( -0.636439417 -0.367448469 0.640642896 ) > then the lattice paremeter should be: A = sqrt (a1^2+a2^2+a3^2) * > alat = 8.05092296 a.u. . > The angle between two vectors can be calculated by: > cosA = a (*) b / |a (*) b|, > where a and b are basis vectors, (*) represents the dot product. > > -- > GAO Zhe > CMC Lab, MSE, SNU, Seoul, S.Korea > > At 2011-11-16 20:14:38,"yedu kondalu" <nykondalu at gmail.com> wrote: > > Dear users, > > I did the optimization for a compound using variable cell > approximation using PWSCF, which belongs to the space group > R3m(160) Rhombohedral representation. The primitive vectors in > terms of lattice parameter a = 8.25791360 a.u. > a(1) = ( 0.619505 -0.357671 0.698774 ) > a(2) = ( 0.000000 0.715343 0.698774 ) > a(3) = ( -0.619505 -0.357671 0.698774 ) > > after completion of optimization step, the primitive vectors > > CELL_PARAMETERS (alat= 8.25791360) > 0.636439417 -0.367448469 0.640642896 > 0.000000000 0.734896938 0.640642896 > -0.636439417 -0.367448469 0.640642896 > > can u please explain me > > how can I calculate the lattice parameter *a* and the *angle > (alpha)* ??? > > Thanks in advance > > Regards > Yedukondalu > -- Gabriele Sclauzero, EPFL SB ITP CSEA PH H2 462, Station 3, CH-1015 Lausanne -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20111117/b8017e8f/attachment.htm