Subject: Re: ZINDO Energy Units

From: "Jason Lye" <[email-masked]>
Date: Wed, 26 Mar 1997 13:31:04 -0500

Hi Netters,

I recently asked how what the energy units were from Zindo, and how to convert
them into something more spectroscopically meaningful such as cm-1.  Thanks to
all who replied.  I have appended Ernest Chamot's reply, although others made
the following clear:

The energy units can be directly converted in the CAChe editor by looking at
the Internals (in the EDIT menu.)

The energy units from a Zindo CI calculation are already in cm-1.

Thanks once again,

Jason Lye

________________________________________________________________

Hi Jason,

Converting the energy units in ZINDO is straightforward.  All the Quantum
Mechanical methods like to use "fundamental" units, in this case, Hartrees.
One Hartree equals 627.51 kcal.  You will notice immediately, that if you
multiply the ZINDO numbers by 627.1, however, that you get a very large
number that doesn't look anything like a heat of formation.  That is because
electronic energies are calculated relative to the completely separated
electrons and nuclei as the reference state, rather than relative to the
elements in their standard state.  This doesn't matter if you are looking at
differences in energies: just subtract one from the other.

I would warn you about the likely accuracy of these energies, however.
ZINDO does okay coming up with energy differences between orbitals for
calculating UV spectra, but it is too crude to calculate good optimized
geometries and corresponding molecular energies.  (Some of the best results
have been obtained by using DFT to calculate geometries, and then ZINDO to
calculate spectra.)  In fact, if you try to calculate heats of formation by
using a ZINDO optimized geometry and subtracting the energies of a ZINDO
optimized molecules of the elements (try something like H2O vs H2 and O2,
for instance) you will find errors in heats of formation on the order of
100-200 kcal/mol!

I'm not sure which energy differences you are looking for.  If you are
looking for vertical excitation energies (in effect just the difference
between how the electrons are distributed at the same geometry, with the
same set of orbitals), then you may be okay, judging by ZINDO's success in
predicting UV absorbances.  If you want to compare the ground state singlet
energy to the energy of the optimized geometry in the triplet state, etc. I
don't think ZINDO will give you a usable accuracy.

Good luck.

EC
---
Ernest Chamot
Chamot Labs, Inc.
530 E. Hillside Rd.
Naperville, Illinois 60540
(630)637-1559
[email-masked]
http://www.chamotlabs.com/cl

---End of forwarded mail from "Ernest Chamot" <[email-masked]>

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_______________________________________________________________________________

Jason Lye,                       |    
Dye Synthesis Research Group,    |    
College Of Textiles,  Box 8301,  |            "Lifes' cheap, but
North Carolina State University, |       the accessories will kill you!"
Raleigh, N.C. 27695 - 8301       |                   
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      Ph:   (919) 515-6615       |                     
      [email-masked]           |         
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From: "Jason Lye" <[email-masked]>
Date: Wed, 26 Mar 1997 13:31:04 -0500

Hi Netters,

Thanks once again,

Jason Lye

Hi Jason,

Good luck.

EC
---
Ernest Chamot
Chamot Labs, Inc.
530 E. Hillside Rd.

-- 

Jason Lye,                       |