GW and BSE at Finite Temperature

[jasonhan0710]

Dear all,

I have noticed that Yambo-5.0 can investigate the optical properties at finite temperature. In the tutorial, at the first step, you did a zero temperature DFT and phonon calculation. However, the atomic structure and phonon structure at finite temperature should be different from that at zero temperature. Do you think we should do a finite temperature molecular dynamics first and get the atomic structure in order to consider the finite temperature effects?

Best,
Jason

[claudio]

Dear Jason,

molecular dynamics (MD) and perturbation theory (PT) are two alternative approaches to include
finite temperature on the electronic structure and optical properties.
If you use MD you have the advantage to include also anharmonic effects difficult to include in PT,
however you need large supercells.
On the other hand if you use PT you include dynamical effects not included in MD,
but you are always within harmonic approximation.
At the end, if you want perform finite temperature calculations with Yambo, just use equilibrium positions at zero temperature
for the atoms.
Finally you have to consider that in some systems thermal expansion can be important, namely
the dilatation of the unit cell, not include in the PT approach, but this effect can be estimated.

best
Claudio