How to use freeh on single-atom radical?

[willows9803]

Hi guys,

I want to calculate the thermodynamic properties of iodine radical. However, since it only has one atom, the gradient calculation gives me nothing. So I couldn't run aoforce and freeh. Is there some way to get the thermodynamic properties of it?

Thank you very much!

[jan]

In fact this is not possible since an atom does not have a vibrational or rotational contributions in the partition sum. This is the reason why
freeH does not output any thermodynamic properties. You could use the Sackur-Tetrode equation to to calculate the entropy of your iodine
radical and and assume that it behaves like an ideal gas to calculate the the free enthalpy. This is explained in any physical chemistry book.
Basicly:
G = U+R*T-T*S
S : You get this from the Sackur-Tetrode eqn.
U: 3/2*R*T for atoms
But your have to keep in mind that this is a rather strong approximation for the iodine radical.

[willows9803]

Thank you very much, Jan!

In fact this is not possible since an atom does not have a vibrational or rotational contributions in the partition sum. This is the reason why
freeH does not output any thermodynamic properties. You could use the Sackur-Tetrode equation to to calculate the entropy of your iodine
radical and and assume that it behaves like an ideal gas to calculate the the free enthalpy. This is explained in any physical chemistry book.
Basicly:
G = U+R*T-T*S
S : You get this from the Sackur-Tetrode eqn.
U: 3/2*R*T for atoms
But your have to keep in mind that this is a rather strong approximation for the iodine radical.