I was trying to relax my monoclinic structure, but after the calculation in the output file the lattice vectors are written instead of lattice parameters for next scf calculation. From the lattice vectors I have calculated the lattice parameters but somehow I am getting wrong
Hello A R Atique Ulla.
This "problem" with lattice parameters is quite annoying. I imagine you set something like a=..., b =..., c=..., etc. Quantum Espresso prefer a description of lattice vectors in a Matrix form, and one constant value, which is multiplied by the matrix. I think this will be the most commom result in the output. What I do is to try to convert these lattice vectors and the constant value into a set of lattice parameters. If you need help with this, let me know.
Best regards,
Ricardo Tadeu
There is no problem with ibrav. The ibrav flag is used for you to tell QE the symmetry of your system. If you use ibrav=0 and define the lattice vectors directly at the CELL_PARAMETERS section, the code will try to figure out the symmetry by itself. Not always it will find all the symmetries of your system because your atoms or lattice vectors might be slightly shifted in relation to the symmetric cell. In order to use an ibrav different of zero you have to express your lattice vectors accordingly to the way that is defined on the pw.x input documentation. For ibrav=-12 you have:
-12 Monoclinic P, unique axis b celldm(2)=b/a celldm(3)=c/a, celldm(5)=cos(ac) v1 = (a,0,0), v2 = (0,b,0), v3 = (c*cos(beta),0,c*sin(beta)) where beta is the angle between axis a and c
You HAVE to be able to express your lattice vectors as v1, v2 and v3 above if you want to use the ibrav=-12 feature. If your vectors are not like that, you will have to transform your cell to the convention above. Once you do that, the lattice parameter is automatically defined, that is, celldm(1) = a (in alat). The output of QE should have the form above, assuming that your first calculation had this convention.
Cheers,
Bruno
Hi Bruno Cucco , thanks for your response, I have relaxed a structure (ibrave=-12), after the relaxation i found the final lattice vector V1 containing z-components, where other two vectors are in usual format. Now my problem is that how can i do scf calculation with these output perameters.
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