TURBOMOLE Modules > Molecular Properties, Wavefunction Analysis, and Interfaces to Visualization Tools

What does the output of freeH mean?

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Dempsey:
Dear Users,

Could you please clarify what some of the values are in the freeH output, there's no information on this in the manual. The value "chem. pot." is consistent with H - TS so I think this is my Gibbs free energy, could you please confirm this? If so, what exactly is this "energy" value? I'm not familiar with the equation given here.

freeh.out:


--- Code: ---           zero point vibrational energy
           -----------------------------
           zpe=   252.3     kJ/mol

   T        p       ln(qtrans) ln(qrot) ln(qvib) chem.pot.   energy    entropy
  (K)      (MPa)                                 (kJ/mol)   (kJ/mol) (kJ/mol/K)

 298.15   0.1000000      17.43    12.00    11.71    150.32    288.52   0.47182

   T        P              Cv            Cp       enthalpy
  (K)     (MPa)        (kJ/mol-K)    (kJ/mol-K)   (kJ/mol)
 298.15   0.1000000     0.1783006     0.1866149    291.00

 ******************************************************
 | qtrans=(m*k*T/(2*pi))^1.5*v h/(2*pi)=1a.u.(omitted)|
 |   m=mol. mass in a.u. v=vol. per mol. of ideal gas |
 | qvib=product(i) 1/(1-exp(-e(i)/kT)                 |
 |   e(i)=frequency of i-th vibrational mode          |
 | qrot=((2*pi*kT)^3*A*B*C)^0.5/(sigma*pi)            |
 |   A,B,C=moments of inertia in a.u.                 |
 | qrot=2*pi*kT*A/(sigma*pi) for lin. mol.            |
 | chem.pot.=ZPE-RT*ln(qtrans*qrot*qvib)              |
 |   ZPE=zero point vibrational energy                |
 | energy=ZPE+3RT                                     |
 |  +sum(i) e(i)*(1+exp(-e(i)/kT))/2*(1-exp(-e(i)/kT) |
 |       =3/2RT for atoms etc.                        |
 | enthalpy=energy+RT                                 |
 | entropy=(energy+RT-chem.pot.)/T                    |
 | const.vol.Heat Capacity : Cv=d(energy)/dT          |
 | const.press.Heat Capacity : Cp=d(enthalpy)/dT      |
 | These formulas are applicable only if              |
 | * rotation can be treated classically              |
 | * the molecule forms an ideal gas/solution         |
 | * the harmonic approximation to vibrational        |
 |   modes is not grossly misleading                  |
 | Electronic (SCF or MP2) energies still have        |
 | to be added to obtain "absolute potentials"        |
 | for chemical equilibrium constants.                |
 ******************************************************

--- End code ---

Thanks,
Dempsey

Arnim:
Hello,

indeed, chem. pot. is the Gibbs free energy.

What is defined as energy can also be called the contributions to internal thermal energy.

Best regards
Arnim

Dempsey:
Dear Arnim,

Thanks for confirming.

Best,
Dempsey

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