# Single electron transfer periodic DFT in VASP

I have the following question: I am currently studying the electrocatalytic CO2RR on Cu materials using periodic DFT calculations and I am using the CHE model to describe the proton electron transfer reactions, as follows:

$$\ce{CO2^* +e- + H+ → COOH^*}$$ $$\Delta G= G(\ce{COOH^*})-G(*)-G(CO2)-G(e^- + \ce{H+})=G(\ce{COOH^*})-G(*)-G(\ce{CO2})-\frac{1}{2}G(\ce{H2}\text{(gas)}$$

Nonetheless, I would like to ask how to describe reactions where I have only an electron transfer for example:

$$\ce{COOH^* +e- → COOH- (aq)}+ *.$$

How do I add calculate the Gibbs free energy of the electron added, as well as how I add the extra electron to the $$\ce{COOH-}$$ (aq)?