From owner-chemistry@ccl.net Tue Nov  1 16:00:01 2016
From: "Osman Mamun mamunm{:}email.sc.edu" <owner-chemistry%x%server.ccl.net>
To: CCL
Subject: CCL: MOPAC: difference between heat of formation and total energy
Message-Id: <-52471-161101140126-17145-fOaYhLBjlODFUNzn2PHmvQ%x%server.ccl.net>
X-Original-From: "Osman  Mamun" <mamunm---email.sc.edu>
Date: Tue, 1 Nov 2016 14:01:14 -0400


Sent to CCL by: "Osman  Mamun" [mamunm . email.sc.edu]
Hello,

I am trying to understand the difference between the reported 'heat of 
formation energy' and 'total energy' in 'MOPAC-2012' version. As I 
understand, it should be Hf=E(total)-E(isol-atom), in that case for any 
isomerization reaction should have equal change in heat of formation 
energy change and total energy change. However, in my calculations, they 
differ by several KJ/mol. Here are my two sample output file:

*******************************************************************
File-1 (reac):
          FINAL HEAT OF FORMATION =       -203.13967 KCAL/MOL =    
-849.93637 KJ/MOL


          TOTAL ENERGY            =      -2668.28858 EV
          ELECTRONIC ENERGY       =     -14596.28160 EV  POINT GROUP:  C1  
          CORE-CORE REPULSION     =      11927.99303 EV
          COSMO AREA              =        179.70 SQUARE ANGSTROMS
          COSMO VOLUME            =        192.03 CUBIC ANGSTROMS

          GRADIENT NORM           =          0.70897
          IONIZATION POTENTIAL    =          9.588044 EV
          HOMO LUMO ENERGIES (EV) =         -9.588  0.710
          NO. OF FILLED LEVELS    =         36
          MOLECULAR WEIGHT        =        180.157

File-2 (prod):
          FINAL HEAT OF FORMATION =       -203.12637 KCAL/MOL =    
-849.88075 KJ/MOL


          TOTAL ENERGY            =      -2668.29051 EV
          ELECTRONIC ENERGY       =     -14597.77515 EV  POINT GROUP:  C1  
          CORE-CORE REPULSION     =      11929.48464 EV
          COSMO AREA              =        179.72 SQUARE ANGSTROMS
          COSMO VOLUME            =        191.93 CUBIC ANGSTROMS

          GRADIENT NORM           =          0.98134
          IONIZATION POTENTIAL    =          9.582592 EV
          HOMO LUMO ENERGIES (EV) =         -9.583  0.716
          NO. OF FILLED LEVELS    =         36
          MOLECULAR WEIGHT        =        180.157

**********************************************************************
According to heat of formation data: reaction energy= 0.05562 KJ/mol
And
According to total energy : reaction energy= -0.1862 KJ/mol

Can anyone please explain what's the difference between this two 
quantities?

Thanks!
Osman Mamun
Graduate student,
University of South carolina