[DFTB-Plus-User] infrared and infrared intensities?

[Benjamin Hourahine]

Hello Marcus,

there is a tool for diagonalizing the mass weighted Hessian on the DFTB+ site
(called modes), this can give you the normal modes.

You could estimate the transition dipole moment using the Mulliken charges,
but you need localized modes for this approximation to be valid (and take care
about periodic boundary condition wrap-around, as this would cause a jump in the value).
The more rigorous method to calculate dipole transitions uses the position of Wannier function 
centres (or several other equivalent methods), and is a long time away from being available,

Regards

Ben


________________________________________
From: dftb-plus-user-bounces at dftb-plus.info [dftb-plus-user-bounces at dftb-plus.info] On Behalf Of Markus Kaukonen [markus.kaukonen at iki.fi]
Sent: 07 January 2011 13:25
To: User list for DFTB+ related questions
Subject: Re: [DFTB-Plus-User] infrared and infrared intensities?

Hei Ben,

I would need periodic boundary conditions.
q=0 phonon mode is fine.

So that is implemented already for my case, also the information for
the intensity?

I only find in manual that the hessian can be calculated, do I have to
code the rest by my self?

Do I also have to calculate the dipole moment by myself based on
muliken charges?

terveisin, Markus

On 7 January 2011 14:51, Benjamin Hourahine
<benjamin.hourahine at strath.ac.uk> wrote:
> Hello Marcus,
>
> do you mean for molecules or periodic solids?
>
> The code can numerically calculate molecule/q=0 phonon modes.
> For molecules the dipole moment is also output by the code,
> you numerically can calculate intensities in this case by numerically
> evaluating the change in dipole moment along the normal
> mode coordinate.
>
> Analytical intensities and periodic systems are a different situation.
>
> Regards
>
> Ben
> ________________________________________
> From: dftb-plus-user-bounces at dftb-plus.info [dftb-plus-user-bounces at dftb-plus.info] On Behalf Of Markus Kaukonen [markus.kaukonen at iki.fi]
> Sent: 07 January 2011 11:53
> To: dftb-plus-user at dftb-plus.info
> Subject: [DFTB-Plus-User] infrared and infrared intensities?
>
> Dear All,
>
> I'd appreciate if someone could give an estimate of the time scale
> when the calculation of infrared spectra and infrared intensities is
> possible with DFTB+
>
> terveisin, Markus
>
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--
--www=http://www.iki.fi/markus.kaukonen
--Markus.Kaukonen at iki.fi
--office: N102 Nano building FIN-02015 TKK
--home: Viinirinne 3 F 12, 02630 Espoo, FIN
--tel: h 045-1242068, w 4518694, 050-5112785
--Rikos ei kannata, eika maatalous
--Suomessa. (Paimio 1998) ---
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