CCL: MOPAC: difference between heat of formation and total energy

 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