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Deploying the output file from a Gaussian frequency calculation to compute ideal-gas thermodynamic functions
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Ideal-gas thermodynamic functions such as molar entropy, heat capacity, and enthalpy content, can be computed easily from the molecular partition function.
Key facts
- Scaling vibrational frequencies by 1.0000 Molecular mass = 117.914 u External symmetry number = 3
- T (temperature in K) S (entropy in J mol-1 K-1) Cp (heat capacity at constant pressure in kJ mol-1 K-1) ddH = H(T)
- H(0) (enthalpy content, in kJ mol-1)
- If you don't want to install the script locally, it's now available on-line (as of Jan. 16, 2004)
- If spin-orbit coupling is ignored, the degeneracy should be 6 for the 2 P ground state
Summary
The rigid-rotor/harmonic-oscillator (RRHO) approximation, adopted here, is popular because it is simple and is often adequate. This information can be used to compute quantities such as temperature-dependent free energies of reaction, delta-G(T). If you don't want to install the script locally, it's now available on-line (as of Jan. 16, 2004). This program is run at a command prompt. If your frequency output file is called " chcl3_freq.out ", then type the following command:.