Based on these convergence behaviors, we adopt the following procedure for determining an optimal embedding space (OES) for all further calculations discussed below. (i) Initially, the DMET fragment consists of the atom to be ionized, plus any first-nearest-neighbor heavy (non-hydrogen) atoms. (ii) If such fragment contains either an oxygen atom of a carboxylic acid or carboxylate functional group, the other oxygen atom is also added to the fragment.(iii)