CCL:G: energy for proton

 Sent to CCL by: Peeter Burk [peeter.burk * ut.ee]
Why not perform the calculation on prorton? With Gaussian 09 (if I remember correctly, then with g03 you had to use Freq=NoRaman to get the same results) you will get: 
 -------------------
  - Thermochemistry -
  -------------------
  Temperature   298.150 Kelvin.  Pressure   1.00000 Atm.
  Atom     1 has atomic number  1 and mass   1.00783
  Molecular mass:     1.00783 amu.
  Zero-point vibrational energy          0.0 (Joules/Mol)
                                     0.00000 (Kcal/Mol)
  Vibrational temperatures:
           (Kelvin)
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
  Sum of electronic and zero-point Energies=              0.000000
  Sum of electronic and thermal Energies=                 0.001416
  Sum of electronic and thermal Enthalpies=               0.002360
  Sum of electronic and thermal Free Energies=           -0.010000
 Peeter Burk
 University of Tartu
 On 04/12/2012 10:17 AM, Tymofii Nikolaienko tim_mail*_*ukr.net wrote:
 
 Sent to CCL by: Tymofii Nikolaienko [tim_mail{=}ukr.net]
 Yes, ZPE is zero.
 However, if considering temperatures higher than 0 K, we can NOT neglect
 the kinetic energy of the proton,
 since its thermal avarage is 3 * kT / 2 !
 It is easy to demonstrate if you run the following for example with H atom:
 # opt freq b3lyp/aug-cc-pVQZ int=ultrafine
 H atom
 0 2
 H 0.0 0.0 0.0
 And than you read in the output file:
 ...
 - Thermochemistry -
 -------------------
 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
 These thermal corrections would be just that same for the proton since
 when calculating thermochemistry Gaussian assumes ground electron state
 only
 (so no electronic degrees of freedom contribute to thermal corrections;
 see http://www.gaussian.com/g_whitepap/thermo.htm ).
 Note that "0.001416" (the "Thermal correction to Energy")
 equals 3/2*k*T
 for T = 298.15 K, while "0.002360" (" Thermal correction to
 Enthalpy")
 equals
 3/2*k*T + k*T since the enthalpy is H = U + P*v while P*v = k*T for
 ideal gas - the model for calculating thermochemistry Gaussian assumes
 (where v is the gas volume per particle). To obtain Gibbs free energy
 use the -T*s term where s is the entropy of ideal gas per particle at
 given temperature.
 Yours sincerely
 Tymofii Nikolaienko
 12.04.2012 8:30, Alexander Bagaturyants bagaturyants-.-gmail.com wrote:
 
 Sent to CCL by: "Alexander Bagaturyants" [bagaturyants_-_gmail.com]
 Dear Arturo,
 Proton has no internal degrees of freedom;
 therefore, its energy is zero, if we neglect its kinetic energy.
 Naturally, the kinetic energy (of a free proton) can take on any value,
 so that we may speak about so-called dissociation threshold.
 A piece of advice: when you consider chemistry,
 you should not sometimes forget about physics.
 Best regards
 Alexander
 
 -----Original Message-----
 From: owner-chemistry+sasha==photonics.ru|,|ccl.net [mailto:owner-
 chemistry+sasha==photonics.ru|,|ccl.net] On Behalf Of Arturo Espinosa
 artuesp|*|um.es
 Sent: 11 April, 2012 21:12
 To: Alexander Bagaturyants
 Subject: CCL: energy for proton
 Sent to CCL by: Arturo Espinosa [artuesp(_)um.es] Dear CCL users:
 I am trying to compute ZPE-corrected dissociation energies for some
 particular bonds, in order to correlate these values with other
 properties computed at the same level (starting from, let's say, B3LYP-
 D/def2-TZVP). My problem (perhaps a bit stupid) comes when dealing with
 heterolytic dissociations of a A-H bond to give A- (anion) and H+ (a
 proton). Moreover I am intending to compare this dissociation with the
 other possible heterolytic dissociation and even with the homolytic
 one. Calculation of the A-H and A- species is straighforward (no matter
 what level of calculation), but the problem is what value (in atomic
 units) should I assign to the H+ species. No QC calculation is possible
 as there are no electrons. I recognize that I am a bit lost.
 Suggestions are wellcome.
 Thank you in advance and best regards,
 Arturo> To recover the email address of the author of the message,
 please
 change the strange characters on the top line to the |,| sign. You can
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