Dear Carlo, You are using the standard setting, taking the B axis as the monoclinic one. Looking at Doc/INPUT_PW.html you will see that quantum espresso takes *C* as the monoclinic axis. For simple monoclinic cells, you just have to perform the permutation 1,2,3 to 3,1,2.
I've lost all hope of understanding base-centered monoclinic systems, and I resort to ibrav=0 in such cases. Regards, Miguel On Wed, 24 Feb 2010 18:52:43 +0100 Carlo Nervi <carlo.nervi at unito.it> wrote: > Dear all, > I did some geometry optimizations with pw.x starting from a > monoclininc cell, using Angstrom and the "A, B, C, cosAB, cosAC, > cosBC" input methods, for example: > > &SYSTEM > ibrav = 12, > A = 8.0828 , > B = 12.5828 , > C = 9.7644 , > cosAB = 0.0d0 , > cosAC = > -0.10713175431387366149628407325294d0 , cosBC = 0.0d0 , > nat = 104, > ntyp = 4, > ecutwfc = 120 , > / > > The input cif file contains the usual a, b, c, and alfa, beta=96.150, > gamma. Therefore, I think, it should be correct to set cosAC as shown > above. However, after open the input file with XCrysden, I realized > that the cell was 90-90-90 (a parallelepiped). > Where I am wrong? > > Playing a little bit with cosAB, cosAC and cosBC I understood that > only cosAB makes the correct angle (96 degrees) to appears in > XCrysden. Therefore I tried another approach: switch b and c, and to > use the celldm() approach. Of course I had to use crystallographic > fractional coordinates and to exchange y with z in the Atomic > coordinates. I'm not sure this is the best approach, but apparently > it works. I would appreciate any suggestions from the community. > > &SYSTEM > ibrav = 12, > celldm(1) = 15.274655166 , > celldm(2) = 1.20797 , > celldm(3) = 1.5567 , > celldm(4) = -0.107131784 , > nat = 104, > ntyp = 4, > ecutwfc = 120 , > / > > Is it normal that pw.x behaves in this way? In other words, are there > any restrictions using the "A, B, C, cosAB, cosAC, cosBC" input > method? > > Thank you in advance, > Carlo > -- ---------------------------------------- Dr. Miguel Martinez Canales Department of Physics & Astronomy University College London Gower Street, London, WC1E 6BT (UK) Fax: +44 207 679 0595 Tlf: +44 207 678 3476 ---------------------------------------- "If you have an apple and I have an apple and we exchange these apples then you and I will still each have one apple. But if you have an idea and I have an idea and we exchange these ideas, then each of us will have two ideas." George Bernard Shaw
