IR spectrum. Help wanted.

[z sh]

Hello everyone,

 I am trying to do vibrational analysis for gas phase system. I am following the tutorial "Calculating Vibrational Spectra from Molecular Dynamics". Initially i have done massive equilibration of a single methanol system for 6000 steps. After that i use the following example CP2k input file to simulating a trajectory with wannier centers for 60000 steps. Then, I calculated the IR spectra with methanol_wannier.xyz file using Travis software. Unfortunately, I don’t get a good IR spectrum because of it doesn’t show peaks at 200, 1000, 1500 and 3700 cm-1 and it has very noise. Would you please guide me why I don’t get a good IR spectrum?

Here i am attaching my IR spectrum and the input files of massive equilibration and the wannier center for a single methanol.

Please help me on this.

Thanks.

[Sam Broderick]

Dear IR-Colleague

6'000 or 60'000? If it is 6'000, that would be the reason.

Otherwise, what were your TRAVIS inputs?

Rgds

Sam

[Sam Broderick]

See fawzi's post on Oct 20, 2010, 1:38:58 PM: Problems of IR and dipole calculation

He recommends looking at the Wannier Center movement and consider centering.

[Thomas Kühne]

Please also check if the Wannier localization has ALWAYS converged. 

In that respect the JACOBI approach is the most robust. 

Best, 

Thomas Kühne

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Dynamics of Condensed Matter

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[Sam Broderick]

Martin Brehm suggested avoiding Wannier localization and to use Voronoi (see spec_tutorial_2018.pdf). Unfortunately this is for a fairly large liquid (R)-propylene oxide cell with 320 atoms.

Currently, I am trying to rework this tutorial for methanol to get a feeling for TRAVIS.

In the tutorial linked above, Martin writes:

"The “&PERIODIC_EFIELD” section controls the external electric field which you will need to
apply for Raman and ROA spectra. The intensity is specified in atomic units. In the tutorial,
we use a value of 5 · 10 −3 a.u. = 2.57 · 10 9 V m −1 , which we found to be a good compromise.
Too small values lead to noisy spectra, whereas too large values might leave the linear regime
of electronic polarizability."