[Pw_forum] calculation of lattice parameter and angle of rhombohedral structure

[Huiqun Zhou]

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








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