Topics

1

General Questions and Answers / Spin Orbit Coupling

« on: February 29, 2016, 14:12 »

Dear All,

         I'm studying a semiconductor (InSb) and need to do calculations on spin orbit coupling. In the tutorial "Noncollinear calculations for metallic nanowires" you give some parameter on calculations for Nickel and pre-calculations for the convergence of values. Are those parameters more or less good approximation to start a calculation on SOC for a semiconductor? I've been looking for information but don't find just a few papers. If you know a good reference or references for this, can you please let me know? Thank you.

Sincerely
Juan

2

General Questions and Answers / Body Centered Tetragonal Brillouin Points

« on: December 21, 2015, 18:43 »

Dear all,

        I'm investigating about the Weyl semimetal. It is a body-centered tetragonal structure. The Brillouin zone on papers is: G, sigma, N, sigma1, Z, G, X. The program just provides G, N and X. I don't know the Z, sigma and sigma1 coordinates. Can you please tell me where I can find the points for these or if you be so kind to provide them? Thank you!

Sincerely
Juan

3

General Questions and Answers / Phase Transition in Materials

« on: September 28, 2015, 17:46 »

Dear all,

I'm studying the BaTiO3 material. Right now, I'm trying to replicate the phase transition from tetragonal (room temperature) to cubic (aprox. 393 K). Using MD, I'm using the ATK-Classical with the parameter set Pedone_2006Fe3 (it also provides the F2). The additional info says that the Brenner and EMT calculators don't have parameters for Barium (same additional info for all the parameters set). I'm using the NVT Berendsen type of MD with the recommended parameters in the tutorial. My questions are:

-If the parameter set I'm using does not have information on the parameters of one of the atoms in my structure, will this affect the results on the calculations? (Lets say Total Energy)

-Is it adequate to use the ATK-DFT calculator using molecular dynamics? I tried using it (just putting the calculator and leaving it with default parameters) but the program was still running after five days! I know some calculations are long but I am not sure if this combination can have something to do with this prolonged time(I'm using a fast machine for this type of calculations). I ran the calculation with the ATK-Classical and it not took so much time.

-I know if there is a change in total energy, there may be a phase change. I would like to know how can I make a graph of TotalEnergy(Temperature). I looked for this in the forum but the only things I found were the ones you provide in the MD tutorial (V(t) and P(t) for the NPT Melchionna) and for the Langevin type, you use the following script:

# Get the kinetic energies
kinetic_energies = md_trajectory.kineticEnergies()
# The number of constrained atoms
number_of_constraints = 10
# Calculate the degrees of freedom in the system
degrees_of_freedom = bulk_configuration.numberOfAtoms() - number_of_constraints
# Calculate the temperatures from the kinetic energies
temperatures = [ke/(1.5*degrees_of_freedom)/boltzmann_constant for ke in kinetic_energies]

I don't know if this can be used for my purpose.

I eagerly wait for your response.

Regards
Juan

4

General Questions and Answers / Bandstructure does not show

« on: August 18, 2015, 15:21 »

Hello!

        I optimized my BiFeO3 rhombohedral structure by relaxing the crystal until 0.001 meV/A force was calculated. I ran the program on a cluster. It never showed any error for the calculation. Once I imported the .nc file to the program to see the bandstructure, the error on the attachment appears.

        I looked in the FAQ and also at the forum but did not find anything about this error. A detail is that, once I hit the "Ok" option, the program opens a bandstructure of another crystal I already calculated the bandstructure. Any help about what I did wrong or what "plugin" I'm missing will be much appreciated!

Thank you!

5

General Questions and Answers / Brillouin Zone Route and Bandstructure Problem

« on: June 21, 2015, 02:09 »

Hello,

        I'm trying to replicate the bandstructure of the BiFeO3 of the following paper,

http://folk.uio.no/ravi/allpapers/85-BiFeO3-prb.pdf

Taking all the computational details in consideration, the parameters I need to build the crystal are on page 5 (I'm doing the R3c structure). When I put all the parameters and go to the brillouin zone route points, it only lets me put G,X when in the paper, the bandstructure is around F, G, Z, F, L, G brillouin points (page 9 fig #8 b).

What I tried was to change the lattice type to triclinic using fractional option. This way the structure stayed almost the same and when putting Brillouin zone route, it gives more variables. Even though I had to use the points T, G, Z, T, Y, G, when checking the bandstructure, it appeared equal although the region of 0 to 6 eV is not equal to the one on the paper.

Even putting the parameters given on the paper, Im not getting the results. Is there something I'm missing on the general parameter calculations? Any recommendation will be great! Thanks!