# How do I get a value of the Gibbs energy of formation at 0 K and 0 bar?

The standard Gibbs free energy of formation for copper(II) oxide, $\ce{CuO}$, is $\Delta_\mathrm fG (\pu{298.15 K},\pu{1 bar}) = \pu{-129.7 kJ mol-1}$.

How can I get $\Delta_\mathrm fG (\pu{0 K},\pu{0 bar})$, the limiting value of this?

I want to compare it with the approximate value obtained by density functional theory calculations:

$$\Delta_\mathrm fG (\pu{0 K},\pu{0 bar}) \approx E^\text{Total}_\ce{CuO} - E^\text{Total}_\ce{Cu} - \frac{1}{2}E^\text{Total}_\ce{O2}$$

• Long story short, you can't. That is, unless you find the heat capacity data for the whole range 0 - 298K and do some integration. – Ivan Neretin Jun 28 '17 at 17:26
• This doesn't make much sense. If you go down to 0K then deltaG is deltaH, so why not compare those? And why not do the calculations for reasonable temperature and pressure and cwork with that? For example if you run a frequency calculation in Gaussian without any keywords you get the values for 298.15 K and 1 atm. – DSVA Jun 28 '17 at 21:00
• VASP takes a different approach to Gaussian (planewaves). So you cannot add temperature and pressure unless you are doing molecular dynamics, which is not the case. – u32004 Jun 29 '17 at 0:21