Iron (Fe) – DFT Study

Crystal Structure:

Fe (BCC)

About/Help

CIF Source:
Wilburn D R, Bassett W A
American Mineralogist 63 (1978) 591-596
Hydrostatic compression of iron and related compounds: An overview
P = 1 Kbar
_database_code_amcsd 0000670

http://rruff.geo.arizona.edu/AMS/download.php?id=00750.cif&down=cif

Simulated Powder XRD using VESTA:

X-Ray Wavelength: 1.54059 Angstrom

Iron (Fe-BCC) Powder XRD Pattern simulation using VESTA

Simulation 1: GGA-Spin Polarized

Pseudopotential Used:

Fe.pbe-n-rrkjus_psl.1.0.0.UPF

PP Type: Ultrasoft
Exchange Correlation Functional: PBE-GGA Spin Polarized
Non-linear core corrections are used.

Wavefunction Energy Cutoff: 45 Ry
Charge Density Energy Cutoff: 495 Ry
k – mesh: 8x8x8
Run Type: GGA-PBE
Starting Magnetization: 0.4

Total Energy vs Cutoff:

Cutoff(Ry)       Total Energy(Ry)

25                      -122.34871192
30                     -122.45867309
35                     -122.46935981
40                     -122.47038821
43                     -122.47173476
45                     -122.47285038
47                     -122.47392017
50                     -122.47514646

In order to perform spin polarized calculations set the nspin parameter to 2.

Then as explained here, set a starting magnetization to break the symmetry. The calculation should find the lowest-energy spin state compatible with the given crystal structure and not orthogonal to initial conditions (e.g.: if you start
with a FM alignment, you will hardly find an AFM final state even if it exists). Perform several calculations at different starting magnetizations, choose the one with smaller energy as ground state. The system must be in all cases treated as a metal, whether it is or not. In principle, you should use pseudopotentials with the nonlinear core correction.

The following shows the total energy for different values of starting magnetization. NOTE: Starting magnetization is given in fractions, ranging between -1 (all spins down for the valence electrons of atom type ‘i’) to 1 (all spins up).

Total Energy vs Starting Magnetization:

SM               Total Energy (Ry)          Tot. Magnetic Mom/Abs. Mg. Mom. (Bohr Magneton)

0.1               -122.47285018               4.53/4.80
0.2               -122.47285038               4.53/4.81
0.3               -122.47285030               4.54/4.81
0.4               -122.47285044               4.53/4.81
0.5               -122.47284975               4.54/4.82
0.6               -122.47285034               4.54/4.82
0.7               -122.47285031               4.54/4.82
0.8               -122.47285014               4.54/4.82
0.9               -122.47285025               4.50/4.82
1.0               -122.47285017               4.53/4.81

Clearly, a starting magnetization value of 0.4 gives the lowest energy.

Now, we perform optimization of geometry.

Optimized Coordinates and Lattice Parameters:

CELL_PARAMETERS {angstrom}

2.828433           0.000000           0.000000
0.000000           2.828433           0.000000
0.000000           0.000000           2.828433

ATOMIC_POSITIONS {angstrom}

Fe           0.000000           0.000000           0.000000
Fe           1.414216           1.414216           1.414216

Total magnetic moment for optimized system: 4.40 Bohr Magneton.

Since there are two Fe atoms in our BCC lattice, therefore, the total magnetization per atom is 4.40/2=2.2 Bohr. Magnt. which is astoundingly very close to the experimental value of 2.2 B.M.

Magnetic moment per atom= 2.2 B.M.

Bandstructure:

Density of States(DOS):

Density of States of Iron (Fe BCC)

 

Input Files:

Fe Input files quantum espresso

Acknowledgements:

I acknowledge the use of the following tools and packages in order to produce the above simulations.
Quantum Espresso(for DFT based simulations): http://www.quantum-espresso.org/
BURAI(for visualization and as a GUI for QE): http://nisihara.wixsite.com/burai
VESTA(for visualization and XRD simulations): http://jp-minerals.org/vesta/en/

References and Resources

http://www.materialsdesign.com/appnote/magnetic-moment-iron

http://www-rjn.physics.ox.ac.uk/lectures/magnetismnotes10.pdf

http://146.141.41.27/Lectures/Omololu-Wednesday-21-MetalsMagnetism2.pdf

 

PhD researcher at Friedrich-Schiller University Jena, Germany. I'm a physicist specializing in theoretical, computational and experimental condensed matter physics. I like to develop Physics related apps and softwares from time to time. Can code in most of the popular languages. Like to share my knowledge in Physics and applications using this Blog and a YouTube channel.



One thought on “Iron (Fe) – DFT Study

  1. Dear Sharma:

    Thanks a lot for this nice tutorial. It’s really helpful. A quick question though: do you know how to get the information of magnetic spin vectors associated with the atoms?

Leave a Reply

Your email address will not be published. Required fields are marked *