Subject: HF ENERGY TO KJ: ANSWER

From: "E. Lewars" <[email-masked]>
Date: Sat, 19 Sep 1998 17:03:55 -0400 (EDT)

1998 Sept 19

Concerning the question:

>                 17-SEP-1998 01:12:30.27
>From:  IN%"[email-masked]"
>To:     IN%"[email-masked]"
>Subj:   CCL:Hartree Fock enegy
>
>
>Hi ccl'ers
>Could someone tell me /point me in the right direction as to where I
>can find a reference as to conversion of Hartree Fock energy to
>KJ/mol.  A reference would also be much appreciated.
>Many thanks
>===============

[This is related to one asked July 30:

Thurs July 30

Yury Voloshin asked

   How can one convert semiempirical energies, in kcal/mol, to hartrees, for
   comparison with ab initio values?]
--

Answer:

     Chemistry studies energy _differences_, not energies.
     To convert ab initio "energies" (energy differencies) to kJ/mol
    (these are just single-point STO-3G energies on MM geometries, but
    they make the point):

       H      H              H      CH3                    Z    -------
        \    /                \    /                             /|\
         C==C                  C==C                               |
        /    \                /    \      (AM1)                   |
      CH3     CH3           CH3     H                    deltaE   |
                                                                  |
      -154.23944 h          -154.24286 h                    E  --------
            Z                        E

     deltaE = -154.23944 -(-154.24286) hartrees
            = 0.00342 h = 2626 x 0.00342 kJ/mol =  8.98 kJ/mol

          (or use 2625.50--I don't think it makes any difference)

          ( h x 627.510 gives kcal/mol)

  It's useful to note that 1 mh (millihartree) is about 3 kJ/mol (2.626),
  then you can see at a glance about how big a given energy difference is.

      E. Lewars
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