[QE-users] ph.x Raman calculations

[Kazume NISHIDATE]

Hi, Jessica

> 2021/03/30 1:53、Jessica Johnson <jj611 at soe.rutgers.edu>のメール:
> 
> I have a very general question about Raman calculations (I will include that I am using QE version 6.4.1 per the posting guidelines in case that helps my answer my question). 


The derivatives of the potential give the T^2 and T^3 dependencies for
the Raman spectrum. To evaluate the quantities there may be two
strategies.

1) Calculate the dynamics at the specified temperature using the
Car–Parrinello MD or the BO-MD and evaluate the specified Raman mode.
The temperature dependencies of the mode, such as the shift and the
width, are the direct results of the anharmonic effects.

2) Evaluate the potential by slightly displacing the atoms following
the Raman mode. The polynomial fit to the obtained potential curvature
will give the third and forth derivatives and you may be able to
evaluate the anharmonicities.


I found the following ref. and hope it gives you a helpful hint.

"Lattice dynamics of anharmonic solids from first principles"
O. Hellman, I. A. Abrikosov, and S. I. Simak
Phys. Rev. B 84, 180301(R) – Published 14 November 2011


best regards
kazume NISHIDATE
敬具　西館数芽

nisidate at iwate-u.ac.jp
kazume.nishidate at gmail.com