TbFe2-Cubic

Dear Materials Project Experts,

I am a physicist and researcher interested in computational materials science, particularly magnetocaloric materials. I have been studying the material TbFe2 and noticed that in your database, there are calculations for electronic properties for the cubic structure (mp-589) but not for the hexagonal structure (mp-1102431).

Could you please explain the reasoning behind this? Is it due to the simplicity of the cubic structure, the direct band gap of cubic phases, the prevalence of cubic structures in applications, or is there another reason?

Additionally, I noticed that the INCAR file does not contain the magnetic moment. Could you please provide guidance on how I can reproduce the calculations using VASP to obtain the ferrimagnetic moment as you produced (3.58 Bohr magneton)?

I appreciate your time and look forward to your response.

Best regards, Sherif Yehia

Thank you for reaching out! Glad to hear that the Materials Project is a valuable resource in your research. I’m tagging @munrojm and @Aaron_Kaplan who might be able to comment on the availability of electronic structure calculations and the workflows for magnetic moment calculations, respectively.

Hi @sherif_Yehia:

Could you please explain the reasoning behind this? Is it due to the simplicity of the cubic structure, the direct band gap of cubic phases, the prevalence of cubic structures in applications, or is there another reason?

We have different computational workflows for computing different properties - right now, all structures, thermodynamic energies, and basic “electronic structure properties” (like on-site magnetic moments) are computed with an r2SCAN meta-GGA relaxation, while band structures are computed with the HSE hybrid functional.

The HSE workflow is many times the cost of the r2SCAN workflow, so it’s used less frequently. There’s no particular reason that we can’t put up band structures for both materials except for the computational cost

All of MP’s calculations are initialized with a ferromagnetic ordering unless a particular AFM ordering is sought. The easiest way to create the VASP inputs from our site is using pymatgen and our programmatic API (mp_api) both installable from pip:

from mp_api.client import MPRester
from pymatgen.io.vasp.sets import MPStaticSet

with MPRester() as mpr:
    structures = {
        str(doc.material_id) : doc.structure for doc in mpr.materials.summary.search(
            fields = ["structure","material_id"], material_ids = ["mp-589", "mp-1102431"]
        )
    }

for mpid in structures:
    if structures[mpid].site_properties.get("magmom"):
        structures[mpid].remove_site_property("magmom")

    vis = MPStaticSet(structures[mpid])
    vis.write_input(mpid)

This will write complete VASP input sets for the two materials you identified, in separate directories.

If you just want the input values of the MAGMOM tag (indexed by element / element+oxidation state if listed), these can be found here.

Dear Aaron_Kaplan

Thank you for your detailed explanation on the computational workflows for different properties. I understand that r2SCAN meta-GGA relaxation is used for computing structures, thermodynamic energies, and basic electronic structure properties, while band structures are computed with the HSE hybrid functional. I also understand that the HSE workflow is more computationally expensive, hence used less frequently.

I appreciate the information that all of MP’s calculations are initialized with a ferromagnetic ordering unless a particular AFM ordering is sought. The code you provided for creating VASP inputs using pymatgen and mp_api is very helpful amazing.

However, I would like to seek some clarification on a few points:

  1. Could you please explain why the code calls for Tb_3 Not Tb for the POTCAR? I understand from the VASP wiki that different versions of PAW potentials exist for some elements, and the choice depends on the specific physical and chemical environment of the atoms in the system. But I would appreciate if you could provide more context on why both Tb_3 and Tb are used in this case. (Please correct me here)

  2. Regarding the precautions for ferrimagnetic materials, I understand that ferrimagnetic materials have populations of atoms with opposing magnetic moments, as in antiferromagnetism, but these moments are unequal in magnitude, so a spontaneous magnetization remains. Therefore, it’s important to accurately represent these unequal moments in the calculations. Could you please elaborate on what specific precautions should be taken in the case of ferrimagnetic materials?

Thank you for your time and I look forward to your response.

Best regards,
Sherif