Yes, that is my mistake. The denominator should be (|a| |b|). Furthermore, I just wanted to say A as the angle between vector a and b~~~ Definitely, in rhombohedral structure, alpha = beta = gamma~
-- GAO Zhe CMC Lab, MSE, SNU, Seoul, S.Korea At 2011-11-17 18:15:17,"Gabriele Sclauzero" <gabriele.sclauzero at epfl.ch> wrote: 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 To:PWSCF Forum 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/20111117/6df9938a/attachment.htm