CCL:G: energy for proton

[David A Case <case++biomaps.rutgers.edu>]

 Sent to CCL by: David A Case [case()biomaps.rutgers.edu]
 On Thu, Apr 12, 2012, Alexander Bagaturyants sasha#photonics.ru wrote:
 >
 > That is, it senseless to calculate formally any thermodynamic function of a
 > free (individual) proton.
 I think "senseless" is too strong a term here.  If you like, you can
 think of
 reactions like AH -> A- + H+ as half-reactions (as in the corresponding
 electron case), and that there will eventually be some proton acceptor in
 a "real" equilibrium experiment.  But this doesn't vitiate the utility
 of
 estimating proton affinities (and gas-phase basicities) as standard
 thermochemical quantities.  Computational estimates using the thermodynamics
 of the free proton can be remarkably accurate compared to experiment; of
 course, the conversion of raw experimental data to standard-state proton
 affinities uses the same model.
 As a side note, it is hard to recommend just using Gaussian or any other
 program to get such values.  The posts that began this thread showed two
 outputs, ostensibly from Gaussian:
 A.  Temperature   298.150 Kelvin.  Pressure   1.00000 Atm.
 ...
  Zero-point correction=                           0.000000 (Hartree/Particle)
  Thermal correction to Energy=                    0.001416
  Thermal correction to Enthalpy=                  0.002360
  Thermal correction to Gibbs Free Energy=        -0.010654
 B.  Temperature   298.150 Kelvin.  Pressure   1.00000 Atm.
  Zero-point correction=                           0.000000 (Hartree/Particle)
  Thermal correction to Energy=                    0.001416
  Thermal correction to Enthalpy=                  0.002360
  Thermal correction to Gibbs Free Energy=        -0.010000
 Note that the Gibbs free energy values differ by a non-negligible amount.
 Of course, no one can ever double-check everything that programs print out,
 but here one can do the calculation by hand; see, e.g.
 http://www.gaussian.com/g_whitepap/thermo.htm.) [I'm not
 sure where how the
 "A" value was computed, although I have some guesses.]
 ...dave case