Dear all, ?I have some trouble in understanding why equivalent (if I am not wrong) representation of the crystal structure leads to different symmetry (as shown in the output from pw.x). All input/output files are attached.
I work with rhombohedral unit cell, alat = 5.46 Ang, gamma =60.36. First, I let PWscf to build lattice vectors using the following settings: ? ? ? ? ? ? ? ? ? ? ? ibrav = 5 , ? ? ? ? ? ? ? ? ? celldm(1) = 10.317903898 ? ? ? ? ? ? ? ? ? celldm(4) = 0.494548768 ...... The code generates lattice vectors: ? ? celldm(1)= ?10.317904 ?celldm(2)= ? 0.000000 ?celldm(3)= ? 0.000000 ? ? celldm(4)= ? 0.494549 ?celldm(5)= ? 0.000000 ?celldm(6)= ? 0.000000 ? ? crystal axes: (cart. coord. in units of a_0) ? ? ? ? ? ? ? a(1) = ( ?0.502718 -0.290245 ?0.814268 ) ? ? ? ? ? ? ? a(2) = ( ?0.000000 ?0.580489 ?0.814268 ) ? ? ? ? ? ? ? a(3) = ( -0.502718 -0.290245 ?0.814268 ) ? ? reciprocal axes: (cart. coord. in units 2 pi/a_0) ? ? ? ? ? ? ? b(1) = ( ?0.994593 -0.574229 ?0.409366 ) ? ? ? ? ? ? ? b(2) = ( ?0.000000 ?1.148457 ?0.409366 ) ? ? ? ? ? ? ? b(3) = ( -0.994593 -0.574229 ?0.409366 ) and shows that ? ?6 Sym.Ops. (no inversion) ? ? point group C_3v (3m) ? ? there are ?3 classes ? ? the character table: ? ? ? E ? ? 2C3 ? 3s_v A_1 ? ?1.00 ?1.00 ?1.00 A_2 ? ?1.00 ?1.00 -1.00 E ? ? ?2.00 -1.00 ?0.00 ? ? the symmetry operations in each class: ? ? E ? ? ? ?1 ? ? 2C3 ? ? ?2 ? ?3 ? ? 3s_v ? ? 4 ? ?5 ? ?6 However, I prefer to work with lattice vectors directly and then changed my settings from : ? ? ? ? ? ? ? ? ? ? ? ibrav = 5 , ? ? ? ? ? ? ? ? ? celldm(1) = 10.317903898 ? ? ? ? ? ? ? ? ? celldm(4) = 0.494548768 to: ? ? ? ? ? ? ? ? ? ? ? ibrav = 0 , ? ? ? ? ? ? ? ? ? celldm(1) = 10.317903898 ? ? ? ? ? ? ? ? ? ?....... ? ?CELL_PARAMETERS ? ? ? ? ? ? ? ?0.502718 -0.290245 ?0.814268 ? ? ? ? ? ? ? ?0.000000 ?0.580489 ?0.814268 ? ? ? ? ? ? ? -0.502718 -0.290245 ?0.814268 CELL_PARAMETERS were taken from the output when I use first settings (see above, crystal axes: (cart. coord. in units of a_0)). ?However, now the code shows different symmetry: 2 Sym.Ops. (no inversion) ? ? point group C_s (m) ? ? there are ?2 classes ? ? the character table: ? ? ? E ? ? s A' ? ? 1.00 ?1.00 A'' ? ?1.00 -1.00 Frankly speaking, I cannot identify what I did wrong. I think, there is a simple explanation, but I failed to find one. Any ideas? Best wishes, -- ===================================== Jess Kondor NSTI ===================================== -------------- next part -------------- A non-text attachment was scrubbed... Name: files2.tar.gz Type: application/x-gzip Size: 5002 bytes Desc: not available Url : http://www.democritos.it/pipermail/pw_forum/attachments/20091217/1642c970/attachment.bin
