Ph.-DOS /transmission eigen values

[Dipankar Saha]

Dr. Julian Schneider,
I wanted to know that_

1) For...obtaining k_ph(T) .....there should be some  del_T between the electrodes {+(del_T)/2  and -(del_T)/2} .... / When we invoke a method called "thermalConductance" on the  "phonon_transmission_spectrum" object .....how these T_L and T_R are set....(say for any specific T= 300 K) ??

2) Besides,  maintaining the same analogy as electron transmission....here,   EI  is replaced by  w² M .....
How this M is formed....??

It will be of great help..if you can please answer those....

Thanks & Regards_
Dipankar

[Julian Schneider]

1) An instead of using finite temperature difference between the phonon occupancies of the reservoirs, the differential ( n_L (T_L) - n_R(T_R) ) / (T_L - T _R) is evaluated as dn(T)/dT at the specified temperature.

2) As it says in the manual M is a diagonal matrix with matrix elements corresponding to the masses of the atoms.

[Dipankar Saha]

Thanks Julian for your reply.....

[Dipankar Saha]

Keeping the same analogy as electron transmission...... EI  is replaced by  w² M ..... / How that is diff. from a case.... where in E²I  ....the E gets replace with h_bar*w ??


Thanks & Regards_
Dipankar

[Dipankar Saha]

Please do reply...!!!
_______
Besides,
Do you calculate the 'dynamical matrix'... with help of the force constant matrix??

[Jess Wellendorff]

You need to consult the ATK manual before asking these questions.

1) http://www.quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.phonontransmissionspectrum.html explains the main parts of the phonon transmission spectrum calculation, including the similarity to the electronic transmission spectrum. It also refers the reader to Ref. 69 for even more details.

2) Yes, as explained in the reference manual, http://www.quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.dynamicalmatrixparameters.html, the dynamical matrix is calculated from the change of all forces on all atoms when all other atoms are displaced a tiny bit.

[Dipankar Saha]

Thanks a lot Jess for the replies ....!!! 
___
However,  in your reply 1) ....you mentioned a tutorial as well  a paper (by Markussen et al.) ...which describe almost the same...as long as the answer to my question is concerned ....!!!

Rather, the answer would have been ....somewhat related to the Eigenvalues of the density matrix....!!! (which you have tried to point out ...as a reply... to my other query)

Anyways.... thanks again.... 

[Dipankar Saha]

By the way...... I think there is a mistake (although trivial...but, still....!!).....in the final expression of thermal conductance as written in the following tutorial__
http://quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.phonontransmissionspectrum.html

Best_
Dipankar

[Dipankar Saha]

As shown in the Fig. attached ..., there occurs a negative freq.  near the gamma point (although,  the 'ASR' and the 'symmetrize'  are checked).  How to avoid this....? ( May be this not due the stability of the struct. .....)

Best_
Dipankar

[Jess Wellendorff]

If this is a phonon bandstructure, negative frequencies implies that the structure is less than perfectly relaxed.

[Dipankar Saha]

I guess not..../ Perhaps, in this case, it might be related to  the accuracy of the numerical calculation...!!!

[Jess Wellendorff]

ok

[Dipankar Saha]

I tried various options_ e.g.,  increasing the repetition in Dij , mesh cutoff etc. ? Only thing left is the "max. interaction range"..... / As it's not out of any classical-potential based calculation....thereby, I'm not quite sure here.... about the value that needs to be set.....
   

[Jess Wellendorff]

Do you use a sufficient cutoff energy and k-point sampling in the relaxation and in the phonon calculation?

[Dipankar Saha]

k-point grid is fine....!!! But, how  to know about the " sufficient cutoff energy"?? Then obviously, you have to look into some other parameters for their convergence...../ I said... I increased the mesh cutoff....; meaning that even with the  lower energy cutoff value...the results (of interest) were already well converged....

Regards_
Dipankar