### 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

## 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):

### 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

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?