[QE-developers] Reduced mass and force constant

[Stefano de Gironcoli]

I wonder if you can elaborate on what is the reduced mass you are 
looking for....

I know what is the matrix of interatomic forces, i know what atomic 
masses are, i know what is the dynamical matrix, I know what are the 
eigenvectors and how to obtain the ones from the others. QE computes all 
these either via ph.x or its partners q2r.x, matdyn.x, dynmat.x ...

I know how to obtain the reduced mass in an isolated dimer or for the 
optical branches at gamma for a 2-atom/cell solid.

for a general mode in a general crystal, if you can provide a definition 
in terms of well defined quantities i'm sure QE (or you from QE output) 
can compute it.

HTH

stefano

On 05/09/22 16:09, Wei Li wrote:
> Dear Quantum Espresso developers,
>
> I would like to compute the reduced mass and force constant for the given frequency obtained by diagonalizing the Hessian matrix. However, QE only gives the interatomic force constant after the phonon calculation.
>
> Just wondering if there is a way to compute the reduced mass and force constant for the given frequency? Not sure if QE has implemented it.
>
> Best,
>
> Wei
> —
> Dr. Wei LI
> School of Chemistry & Materials Science, Hunan Agricultural University
> Changsha, 410128, PR China
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