Subject: Summary: UV-Vis spectral simulations

From: <[email-masked]>
Date: Wed, 17 Jul 1996 01:38:51 +0200

Original query:

>An associate has asked me to find out what software may be available for
>simulation or computation of UV-visible spectra, given only a structure.  He is
>interested in calculating absorption maxima (transition frequencies),
>extinction coefficients, and (if possible) envelope shapes.
>
>From Zerner's discussion of INDO/S in Volume 2 of "Reviews in Computational
>Chemistry," most, if not all, of this can be calculated at the semi-empirical
>level.  Has this capability been included in a reasonably easy-to-use package
>which would require minimal post-processing to obtain results interpretable by
>us computationally challenged types?

I have received a number of replies.  Several commercial packages have the
capability to do the computation of the frequencies and oscillator strengths
(related to relative values of the extinction coefficient).  Users of some of
the packages also replied reporting their good experience.  Most packages
feature some sort of interface to the ZINDO program (INDO/S), with additional
semi-empirical or _ab initio_ methods available. . .consult your sales rep.
Packages mentioned include Spartan, Hyperchem, CAChe WorkSystem; MSI weighed in
with a ZINDO interface.  Comments from the users:

>>Ernest Chamot ([email-masked]):
ZINDO (with the INDO/S parameters) does indeed calculate all you need to
construct a normal looking UV-visible spectrum including frequencies and
extinction coefficients.  For ease of use, I highly recommend the
implementation of ZINDO in the CAChe WorkSystem (a commercial package from
Oxford Molecular): just draw the molecule, and then either select CI
calculation from a ZINDO dialog box (if you want to do things manually) or
choose UV-vis spectra/excitation energy from the standard procedures
provided in their molecular spreadsheet, ProjectLeader.  The only "post
processing" is that when you visualize the molecule you will also have the
option of displaying the calculated UV spectrum. (You will also be able to
click on an absorbance in the spectrum to see the part of the molecule
involved with that transition highlighted.)  The "envelope shape"
calculation is fairly simple, though.  It just assumes a normal "peak width"
(which you can vary if you wish.)

So far as ZINDO's accuracy in reproducing experimental UV-vis spectra, it
can do very well with transition metal complexes (which it was specifically
parameterized for) and is pretty good for many organic systems with extended
conjugation, but it sometimes does poorly with systems containing nonbonded
electron pairs.  (This makes it especially important that you validate your
calculations against some related systems, and you may need to calibrate
frequencies or just focus on differences rather than absolute frequencies.)

>>Edgardo Garcia ([email-masked]):
We have Hyperchem 4.0 and it calculates the UV (frequencies) and IR
spectra and normal mode animation, by some semi-empirical methods, also
it's VERY easy to use.  It's only weakness is the limited output control.
I guess a program called Cache also does this sort of thing and
it's easy to use.

>>Brian Williams ([email-masked]):
I am also new to comp chem, but have found the Hyperchem package a
reasonable way to get at UV-visible spectra.  I am running this on a 120
Pentium, as as long as you are not in a big hurry, or have a system with
too many atoms, I find I can generally get useful info to compare with
experimental data. If you have a workstation, you could probably do
things much faster on larger systems.

There was one package I had not heard of -- StrukEd (also a Lite version) for
which contact information:
     StrukEd-Lite is available from:
     Umschau Verlag
     POB 1247
     D-58207 Schwerte (Germany)
             Fax +49-2304-83271
             Phone       -81854

    (StrukEd is not expensive, DEMO version is available for approx. 20.-DM)
    For more details you can see the WWW information
    http://ibm530.chemie.uni-halle.de/usr.www.software.htm
    [email-masked]

And finally, Chemical Concepts (contact [email-masked]) has a PC package
called SpecTool -- This does the wavelength calculation by the group
contribution/additive method.