15 June 2012

193. Notes on UV/VIS - TD DFT in nwchem

I've been interested in looking at using NWChem to predict UV/VIS spectra. This post doesn't show how to do it but is rather just a look at what affects the positions of absorbances.
(although it more or less just involves
tddft
       cis
       nroots 24
end
task tddft energy)
I chose benzene and water as test cases. 

Here's water:
water

Reference spectrum in gas phase: http://www.lsbu.ac.uk/water/vibrat.html (166.5 nm) which tallies very well with 3-21g and 6-31g, but not at all with 6-31++g** or 3-21++g*.

Here's benzene:

Reference spectrum: http://www3.wooster.edu/chemistry/is/brubaker/uv/uv_spectrum.html
The reference spectrum, while a bit diffuse, shows the main absorbance at ca 178 nm. Presumably that's in benzene, not water.

More basis sets:


(cat Benzene_631g/Outputs/nwch.nwout |egrep "Root|sci"|gawk '{print $4,$6}'>bz631g.dat)

2 comments:

  1. Hi,

    What the level of theory used?

    All the best,
    Felipe

    ReplyDelete
    Replies
    1. the NWCHEM implementation of b3lyp. Looking back it would've been more informative and effective to vary the XC rather than the basis sets (e.g. the big difference in the performance of CAM-B3LYP vs most standard hybrid functionals is well-known)

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