Keyword THERMO

This keyword activates the calculation of thermal corrections to thermodynamic functions. It can be used only in combination with the FREQUENCY keyword (see Section 4.8.1).
Options:

	MAX=$<$Real$>$		Maximum temperature. The default is 2000 K.
	MIN=$<$Real$>$		Minimum temperature. The default is 100 K.
	INT=$<$Real$>$		Temperature interval. The default is 100 K.
	VIBONLY		Restrict calculation to vibrational contributions plus zero point energy.

Description:
The thermal corrections to thermodynamic functions are calculated in the approximation of the ideal polyatomic gas [241]. For diatomic molecules, a ro-vibronic correction term is included. Electronic contributions are neglected. The temperature range can be specified with the options MAX and MIN. To avoid numerical instabilities, the minimum possible temperature is fixed to 5 K. The step size of the temperature interval is defined by the option INT. The output contains the heat capacities $c_p$, the entropy correction $\Delta S$, noted by S, the enthalpy correction $\Delta H$, noted by H, and the internal energy correction $\Delta U$, noted by U, for each temperature step. The natural logarithm of the partition function $z = z_{trans} z_{rot} z_{vib}$ is also reported. Note that zero point contributions are not included. These are given elsewhere in the output. Thus, $\Delta H$ and $\Delta U$ go to zero for $T \rightarrow 0 K$ as the following output for CO$_2$ shows.

 THERMODYNAMIC FUNCTIONS (EXCLUDING ZERO-POINT ENERGY)

   T[K] Cp[J/(K*MOL)] S[J/(K*MOL)] H[KJ/MOL] U[KJ/MOL] ln (z)


    5.0     29.10        97.76        0.15      0.10    63.01
  100.0     29.23       184.95        2.91      2.08    73.50
  200.0     32.68       206.03        5.97      4.31    75.94
  300.0     37.58       220.23        9.49      7.00    77.44
  400.0     41.59       231.61       13.46     10.13    78.57
  500.0     44.76       241.24       17.78     13.62    79.49
  600.0     47.34       249.64       22.39     17.40    80.29

The VIBONLY option restricts the energetic contributions to the internal degrees of freedom (vibrational contributions). Thermodynamic functions calculated with this option enabled include the vibrational zero point energy as the following CO$_2$ output shows.

 VIBRATIONAL THERMODYNAMIC FUNCTIONS (INCLUDING ZERO-POINT ENERGY)

   T[K] Cp[J/(K*MOL)] S[J/(K*MOL)] H[KJ/MOL] U[KJ/MOL] ln (z)


    5.0      8.31         0.00       30.27     30.27   -728.24
  100.0      8.45         0.02       30.28     30.28    -36.41
  200.0     11.89         0.92       30.43     30.43    -18.19
  300.0     16.79         3.32       31.03     31.03    -12.04
  400.0     20.80         6.33       32.09     32.09     -8.89
  500.0     23.97         9.47       33.50     33.50     -6.92
  600.0     26.56        12.56       35.20     35.20     -5.55