Subject: Re: CCL:ZINDO "Heats of formation"

From: [email-masked] (Joel Polowin)
Date: Fri, 27 Oct 95 11:55:25 -0400

> Date: Thu, 26 Oct 95 18:06 CDT
> From: "George P. Ford"  <[email-masked]>
> 
> Joel Polowin writes:
> 
>> My calculations with HyperChem for benzoic acid gave heats of formation of
>> -68.1 kcal/mol for AM1, -66.4 kcal/mol for PM3, and -3147.6 kcal/mol for
>> ZINDO/1.  ZINDO/S did not converge.

PLEASE get the quoting levels right, especially for a matter like this!  The
following was by Paddy Kane, NOT by me!

>>> Why are the ZINDO/1 and ZINDO/S methods giving me such apparently
>>> incorrect values?
> 
> I am not a Hyperchem user, but surely the answer is that the ZINDO data are
> total energies, not heats of formation at all.

I repeated the calculation -- optimized with AM1, then a ZINDO/1 single
point calculation on that geometry, then the ZINDO/1-optimised structure.

AM1-optimised:
Total Energy                        =  -37355.0409466 (kcal/mol)
Total Energy                        =   -59.527858396 (a.u.)
Binding Energy                      =   -1696.0933786 (kcal/mol)
Isolated Atomic Energy              =  -35658.9475680 (kcal/mol)
Electronic Energy                   = -151629.7883320 (kcal/mol)
Core-Core Interaction               =  114274.7473854 (kcal/mol)
Heat of Formation                   =     -68.1333786 (kcal/mol)
Gradient                            =       0.0071126 (kcal/mol/Ang)

ZINDO/1 single-point on that structure:
Total Energy                        =  -52247.3049941 (kcal/mol)
Total Energy                        =   -83.259717950 (a.u.)
Binding Energy                      =   -4768.6141418 (kcal/mol)
Isolated Atomic Energy              =  -47478.6908523 (kcal/mol)
Electronic Energy                   = -181378.3981024 (kcal/mol)
Core-Core Interaction               =  129131.0931083 (kcal/mol)
Heat of Formation                   =   -3140.6541418 (kcal/mol)
Gradient                            =      49.3096263 (kcal/mol/Ang)

ZINDO/1-optimised:
Total Energy                        =  -52254.2264407 (kcal/mol)
Total Energy                        =   -83.270747757 (a.u.)
Binding Energy                      =   -4775.5355884 (kcal/mol)
Isolated Atomic Energy              =  -47478.6908523 (kcal/mol)
Electronic Energy                   = -181134.0697328 (kcal/mol)
Core-Core Interaction               =  128879.8432921 (kcal/mol)
Heat of Formation                   =   -3147.5755884 (kcal/mol)
Gradient                            =       0.0101942 (kcal/mol/Ang)

Heats of formation are calculated as (binding energy) - (sum of atomic
heats of formation); binding energy = (total energy) - (isolated atomic 
energy).

Joel

------------
Joel Polowin, Ph.D.   Manager, Scientific Support
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