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:

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

  • 1
    $\begingroup$ 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. $\endgroup$ Jun 28, 2017 at 17:26
  • $\begingroup$ 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. $\endgroup$
    – DSVA
    Jun 28, 2017 at 21:00
  • $\begingroup$ 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. $\endgroup$
    – user32004
    Jun 29, 2017 at 0:21


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy