Messages

31

General Questions and Answers / Re: fermi level problem

« on: May 12, 2016, 16:07 »

I checked OMX and it seems much better.... but also quite hard pseudo
Waiting impatiently for new pseudo release:-)

Thanks for your help
Cyrille

32

General Questions and Answers / Re: fermi level problem

« on: May 12, 2016, 15:24 »

Tier0 has some localized 3s and 3p.
But it only includes 4s and no 4p.
I do not know if it is the origin of my problem but the strongly dispersive "4s" parabolic band, crossing the 3d has a minimum (below -10eV) which seems to me too low. It is typically 2 eV below  other DFT results..

Of course it would much preferable not to have the costly 3s and 3p but having 4s and 4p...
However the FHI pseudo/basis give very bad results for Cr.

Cyrille

33

General Questions and Answers / Re: fermi level problem

« on: May 12, 2016, 14:37 »

It's me again..
Forget about my post it seems to be again related with the pseudo/basis...

I will do some additional tests..

Cyrille

34

General Questions and Answers / fermi level problem

« on: May 12, 2016, 13:16 »

Dear all

I am performing calculations on a structurally very simple but magnetically very complicated system: FeCr in B2 structure.
B2 structure is just based on bcc structure but Fe is sitting at the corner of the cube and Cr at the centre (or vice versa:-) so it is simple cubic.
Since I realized that FHI pseudo/basis was doing a very bad job (in fact totally wrong) I am using HGH pseudo (Tier0)
Now the magnetization of the system is very reasonable (in agreement with other DFT results) but when I plot the band structure I am convinced that the Fermi level is not at the right position.
Indeed the band structure looks very reasonable but the Fermi level (zero of energy) is clearly too high.
I wonder if someone has experienced this type of problem.

I have attached my input and log file..

Thanks in advance

Cyrille

35

General Questions and Answers / Re: ProjectionList and angularMomenta..

« on: March 1, 2016, 15:04 »

Yes exactly.
Then you can also see how the molecular levels are broadened by interaction with substrate.

Cyrille

36

General Questions and Answers / Re: ProjectionList and angularMomenta..

« on: March 1, 2016, 14:32 »

By the way there is another interesting (but more involved) feature related to my previous post: the possibility of calculating the density of states projected on a given molecular orbital. This can be very useful for instance to analyse  electronic features of a molecule deposited on a surface.  One can calculate first the MO of the isolated molecule and then calculate the PDOS (on these molecular orbitals) when this molecule is in contact with a surface..

It has been implemented in QE and proved to be very useful..

thanks a lot for all your work.

Cyrille

37

General Questions and Answers / Re: relaxation+spin

« on: February 29, 2016, 12:01 »

OK thanks Daniele that's clear.
I can increase the number of electronic scf step to be (almost) sure that I do not encounter this situation again.

Cyrille

38

General Questions and Answers / Re: ProjectionList and angularMomenta..

« on: February 26, 2016, 11:43 »

OK thanks
Maybe in a future version of atk:-)

Cyrille

39

General Questions and Answers / ProjectionList and angularMomenta..

« on: February 26, 2016, 10:58 »

Dear all

I wanted to write a script to calculate the density of states that is not only decomposed in term of anglular momenta (l=0,1,2) but also in terms of magnetic number m or more precisely in real harmonics px,py,pz (same for d..).
Is there an easy way to extract to do that?

thanks in advance

Cyrille

40

General Questions and Answers / relaxation+spin

« on: February 26, 2016, 09:51 »

Dear all

I have a funny problem when trying to relax a molecule (or more precisely a 2D network of molecules).
I have fist performed a spin polarized calculation LSDA and everything goes well. The relaxation is smooth and II get a magnetic solution. Then I have tried to do a non magnetic calculation. But instead of using LDA I have used LSDA and starting from zero magnetization. The first scf cycle does not converge (after 100 iterations) but the calculation continues anyway (after forces have been evaluated and system relaxed). However in this new scf cycle the system has acquired a magnetization as if a "random magnetic kick" had been given to the system... Finally the relaxation continues and at the end the system converges towards the magnetic solution..

Why is it so?

Thanks in advance

Cyrille

41

General Questions and Answers / Re: Adding a small imaginary part to Self-energy

« on: November 17, 2015, 15:51 »

Let me put my question more precise.
Where does the Infinitesimal parameter (set to 10^-6eV by default) enter?

If I am correct it enters as a small imaginary part in the calculation of the "surface"  Green functions used to obtain the self-energies.
But it does not enter in the Central Green function?

which reads:
GC(z=E+i epsilon)=1/(E-Sigma(E+i epsilon) )
and not
GC(z=E+i epsilon)=1/(E+i epsilon-Sigma(E+i epsilon) )

Cyrille

42

General Questions and Answers / Re: Adding a small imaginary part to Self-energy

« on: November 13, 2015, 14:57 »

One more question:

Is the infinitesimal parameter added only in the calculation of the Leads self-energies or is it also added in the calculation of the Central part Green function.
More precisely do you have
GC=(ES-H-SigmaL-SigmaR)^-1
or
GC=((E+i epsilon)S-H-SigmaL-SigmaR)^-1

Cyrille

43

General Questions and Answers / Re: Adding a small imaginary part to Self-energy

« on: November 13, 2015, 11:25 »

I was thinking that in a first very simple approximation I could just increase the "infinitesimal" value for the calculation of the self-energies.
If I understand well  it should add a constant (in energy but diagonal in "space") term.
Of course the next step could be to add a term that also depends on the energy!

Cyrille

44

General Questions and Answers / fixed spin in transport calculations?

« on: November 12, 2015, 13:54 »

Dear all

I have recently managed to perform fixed-spin calculations (angle of the spin set to a given value) for an Iron wire with SOC (OMX pseudo/basis)
For the moment it is only a "standard" DFT calculation with "BulkConfiguration"
I could set the spin orientation by using the following script (taken from FeMgO.py)
==================================================
B0 = 5*eV
theta=30*Degrees   
#----------------------------------------
# Intial spin
#----------------------------------------   
spin_list = [(Iron, 1, theta, 0*Degrees)]
initial_spin = InitialSpin(scaled_spins=spin_list)
spin_list = [(Iron, theta, 0*Degrees)]
fixed_spin = FixedSpin(spin_list, B0)

bulk_configuration.setMagneticField(fixed_spin)
=========================================================
The calculation works perfectly fine. In particular I am able to follow the evolution of the band-structure with the angle between spin and wire axis...

I now try to do the same type of calculation but in transport (DeviceConfiguration) in order to study the evolution of the transmission with the angle of the spin (AMR),
But my calculation crashed.

Is the option .setMagneticField(fixed_spin) available in DeviceConfiguration?

Thanks in advance

Cyrille

45

General Questions and Answers / Adding a small imaginary part to Self-energy

« on: November 10, 2015, 14:12 »

dear all

I was wondering if there was a "simple way" to tweak atk in order to add an imaginary part to the self-energies.
This could be a poorman solution to deal with various scattering processes...

thanks in advance

Cyrille