Heey Smita Patir

I would say that structure optimization sets the basis for all the subsequent steps in your process, and skipping it may lead to inaccurate results, as you need well-relaxed structures to capture correct band features. Instead, do relax or vc-relax first to minimize forces and stress. Also, after the SCF, do NSCF to refine the electronic states over a denser k-mesh before moving on to the band calculation. Yet, if the atomic positions or lattice parameters are far off, forces and stresses in the system may be too high, and as a consequence, you'd have convergence issues during the SCF.

Best,

Gabriel Vinicius

Gabriel Vinicius Thank you so much for your helpful response!

Can you describe an input file, especially for a monoclinic system(ibrav=-12)? The input parameters..like celldm ..is this to be used in bohr? Also ATOMIC_POSITIONS (crystal) means the fractional coordinates obtained from the CIF file? Some calculations are done from scratch without giving the etot convergence values in the &control section, why ? k-points {crystal_b } format? As I am new to this field, I'm finding it hard to grasp.

np, glad to help.

I will try to address your questions. The celldm(1) should be specified in Bohr units; celldm(2), celldm(3) are the ratios of lattice parameters to a, and celldm(4) is cos(beta), where beta is the monoclinic angle between the a and c lattice vectors*. This is specific to your case, a monoclinic lattice. The ATOMIC_POSITIONS are, in fact, fractional coordinates obtained from the CIF file (as I first learned how to code on VASP, I take what I need from the POSCAR file, instead). Sometimes, convergence thresholds like etot_conv_thr and forc_conv_thr are not set explicitly because the default values are sufficient, so no need to specify them. The K_POINTS {crystal_b} defines a Monkhorst-Pack k-point grid in fractional (reciprocal lattice) coordinates.

*retrived from https://www.quantum-espresso.org/Doc/INPUT_PW.html

See if that helps,

Best,

Gabriel Vinicius

Gabriel Vinicius Thank you once again, Gabriel. I have more questions for you..

How to choose the ibrav numbers and the unique axes for monoclinic crystal system by looking at the cif file..ibrav = 12, -12, 13 or - 13...celldm(5)= cos (ac), which means cos(beta in degree)?

k_points{crystal_b}

5

L 20

gG 20

X 20

K 20

gG 20...these values (20) can be set to any desired values and can be manually specified as input?

Heey Smita Patir

I’m not very familiar with using CIF files directly. I suggest downloading the VESTA software and opening the CIF file there. Then, go to File > Export Data and select VASP file as the file type. Open the exported file in any text editor. This way, you'll have everything you need in a straightforward format. If you prefer, you can send me the CIF file, and I can do it for you. The way you set up the k-mesh looks odd to me, is this intended for structure relaxation?

Best,

Gabriel Vinicius

Gabriel Vinicius I used the K-mesh specified in the 'bands' calculation based on an example I found online. I will definitely download the recommended software, but in the meantime, I am attaching a CIF file and would greatly appreciate any insights you can provide.

Please find attached the VASP POSCAR file named FeBiO3.vasp and a possible input file for your structure relaxation in QE, FeBiO3.in. Note that I filled the input file with information obtained from the POSCAR file, which was derived from your CIF file.

I used standard settings for the relaxation parameters. Try it and see if it works for you. You may want to adjust them according to your needs.

Hope that helps you clarify some stuff :)

Cheers

Gabriel Vinicius

Gabriel Vinicius Thank you very much Gabriel! I really appreciate your time and expertise. I'll certainly reach out again if I come across any further questions or challenges related to this topic.