Subject: AM1 under GAUSSIAN ???

From: ACKERMANN Lutz GRL <[email-masked]>
Date: Thu, 19 Feb 1998 18:26:39 +0100

Dear Netters,
we have recently carried out a series of calculations
using MOPAC/AM1.  When we asked academic partners to do some ab initio 
calculations on the same set of compounds we were surprised to find, that 
there
seems to be an inconcistency between GAUSSIAN/AM1 and MOPAC/AM1,
concerning the heat capacity Cp. Does anyone know, if this is:
 -> a well known phenomenon/problem/bug
 -> a consequence of a different implementation (deliberate) or
 -> one of the great mysteries of life?

For your orientation I have appended parts of the MOPAC and GAUSSIAN output
of calcs for the CO2 molecule.

Best  Regards

Lutz Ackermann

_________________________________________________________
Dr. Lutz Ackermann

Service Chimie Physique, Groupment de Recherches de Lacq
elf atochem
R.N 117, B.P. 34, F-64170 Lacq (France)
Phone: (0033) 5 59 92 67 66   FAX: (0033) 5 59 92 67 65
e-mail: [email-masked] or [email-masked]

or

phone/FAX: (0033) 5 59 27 65 43
[email-masked]
___________________________________________________________

CO2 (AM1)

MOPAC 6.0:
 ----------
                    CALCULATED THERMODYNAMIC PROPERTIES
                                          *
   TEMP. (K)   PARTITION FUNCTION   H.O.F.    ENTHALPY   HEAT CAPACITY 
 ENTROPY
                                    KCAL/MOL   CAL/MOLE    CAL/K/MOL 
  CAL/K/MOL

    273  VIB.          1.139                   203.06527    2.22755 
   1.00258
           ROT.     255.                        542.522      1.987 
    12.997
             INT.     290.                        745.587      4.215 
    14.000
           TRA.         0.248E+27                   1356.305      4.968 
    36.817
           TOT.                       -80.062  2101.8922     9.1830 
   50.8170

    298  VIB.         1.181                   261.82494    2.46932 
   1.20837
         ROT.     278.                        592.203      1.987     13.172
         INT.     328.                        854.028      4.457     14.380
         TRA.    0.282E+27                   1480.509      4.968     37.252
         TOT.                       -79.829  2334.5371     9.4247    51.6320

GAUSSIAN:
 --------

 ...

Energy=   -0.127281006429 NIter=   9.

 ...

                    E (Thermal)             CV                S
                      KCAL/MOL        CAL/MOL-KELVIN    CAL/MOL-KELVIN
 TOTAL                    9.040              7.411             51.623
 ELECTRONIC               0.000              0.000              0.000
 TRANSLATIONAL            0.889              2.981             37.270
 ROTATIONAL               0.592              1.987             13.171
 VIBRATIONAL              7.559              2.443              1.182
 VIBRATION  1             0.886              1.182              0.586
 VIBRATION  2             0.887              1.179              0.583
 ...

Transforming the Energy given by GAUSSIAN from Hartree to kcal/mol, one
gets -79.8653 kcal/mol, which is close to the Heat of Formation calculated
from MOPAC (at 298K), -79.829 kcal/mol. The entropy is also very similar 
between
the two programs, but the heat capacity differs a lot ( 7.411 CAL/MOL-KELVIN 
in
GAUSSIAN vs. 9.4247 CAL/K/MOL in MOPAC!!???