Subject: CCL: AM1 energies in Gaussian-92

From: Tony Dyson <[email-masked]>
Date: Thu, 09 Jun 1994 10:59:53 +1000

We are currently using the AM1 semi-empirical HF model in Gaussian 92
in order to study some systems that are too large for the ab initio
methods. My query regards the total energy reported by Gaussian for
the SCF procedure.

To illustrate, I have performed an energy calculation for the
acetylene molecule using both STO-3G and AM1.

The STO-3G calculation yields this:

 SCF DONE:  E(RHF) =  -75.8541542129     A.U. AFTER    7 CYCLES
             CONVG  =     .7766D-08             -V/T =  2.0045
             S**2   =    .0000
 KE= 7.551786283317D+01 PE=-2.270732528251D+02 EE= 5.080104338819D+01

while the AM1 calculation yields this:

 It=  1 PL= 6.73D-01 DiagD=T ESCF=     37.414799 Diff=-5.95D-01 RMSDP= 4.47D-01.
 It=  2 PL= 4.62D-02 DiagD=T ESCF=     25.087786 Diff=-1.23D+00 RMSDP= 1.18D-02.
 It=  3 PL= 1.68D-02 DiagD=F ESCF=     23.900704 Diff=-1.19D-01 RMSDP= 6.01D-03.
 It=  4 PL= 1.54D-03 DiagD=F ESCF=     23.677267 Diff=-2.23D-02 RMSDP= 3.66D-04.
 It=  5 PL= 6.06D-04 DiagD=F ESCF=     23.751946 Diff= 7.47D-03 RMSDP= 1.42D-04.
 It=  6 PL= 2.32D-04 DiagD=F ESCF=     23.751787 Diff=-1.60D-05 RMSDP= 9.29D-05.
 It=  7 PL= 1.44D-05 DiagD=F ESCF=     23.751739 Diff=-4.81D-06 RMSDP= 3.46D-06.
 It=  8 PL= 4.45D-06 DiagD=F ESCF=     23.751758 Diff= 1.90D-06 RMSDP= 1.17D-06.
 It=  9 PL= 1.66D-06 DiagD=F ESCF=     23.751758 Diff=-1.13D-09 RMSDP= 6.00D-07.
 Energy=     .087287803312 NIter=  10.
 Dipole moment=   .000000   .000000   .000000

The result E(RHF) = -75.85 au from the STO-3G calculation is the kind of thing
I expect to get from the calculation. Where is its equivalent in the AM1 output
file? Is it Energy = 0.087?  If so, what units does this number have? And why
is it a positive number?

I'm sure this question has a very simple answer, but I've searched the G92
manual and can't find what it is. Our own in-house semi-empirical programs all
give results in Hartree atomic units, and GAMESS gives its results in eV. Can
anybody explain to me how to interpret these Gaussian results?

Regards,
		Tony Dyson

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Anthony J. Dyson                                 _________
Theoretical Surface Physics Group                _|__o__|_
University of Newcastle	                         _|_(/)_|_
Australia                                           d-b

		     "I'd rather be flying!"
        		              Anonymous

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