The standard correction method is only applied to when the corrected elements appear in a negative oxidation state, but this requires guessing the oxidation states of each species in the compound in order to compute the correction to the formation energy. Oxidation states are not trivial to guess for many structures, especially ones with semi-metals and non-metals that can exist in polyatomic anions, like chlorate. The standard correction method uses pymatgen's bond valance analyzer, then pymatgen's oxi_state_guesses method, then a maximum electronegativity method to guess the oxidation states. The methods are attempted in that order, so oxi_state_guesses is only used if BV-Analyzer fails, and maximum electronegativity is only used if both BVAnalyzer and oxi_state_guesses fail.