[Pw_forum] Is it possible to calculated IR and Raman spectra for molecules adsorbed on metal surfaces

[Ari P Seitsonen]

Dear Jibiao Li,

   A late reply, but: It is not possible to "isolate" the molecule in the 
calculation nor in the experiment, as any photon hitting the system might 
cause an electronic excitation, either at the molecule or the surface, so 
the intensity of the spectrum would be beyond the non-resonant regime.

   The crude approximation is to calculate the vibrational modes and try to 
correlate those with experiments - without the intensity (but maybe with 
the selection rules from symmetry). Next, you might try to move the atoms 
along the normal modes and see if you get something useful from the 
variation/derivative of the dipole/polarisability. But, as said, also in 
the experiment there could be any excitations, thus smearing the 
intensities.

     Greetings from Paris,

        apsi

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   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
     Ecole Normale Supérieure (ENS), Département de Chimie, Paris
     Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935


On Tue, 9 Jan 2018, jibiaoli wrote:

> Dear All,
> 
> I learned from the maillist that pure metallic systems do not have IR and Raman active modes, thereby it's meaningless to calculated IR and Raman
> spectra for those systems. However, I am very much interested in molecules adsorbed on metal surfaces, is it possible to get IR and Raman spectra
> for molecules/metal systems through QE calculations?
> 
> Best
> 
> Jibiao Li
> 
> Yangtze Normal University, China
> 
>