To verify this hypothesis, we estimate the number of hypothetical charge-neutral PS compositions with the SMACT package . For ternary PSs, the result is 1,737 distinct compositions assuming M a P b S c formulas including metals up to Bi and stoichiometric coefficients a,b,c between 0 and 10. For comparison, the number of charge-neutral ternary oxysulfides (M a O b S c ) is only 228 using the same rules. For quaternary PSs, the number of distinct charge-neutral composition is 202,829, assuming M1 a M2 b P c S d formulas with stoichiometric coefficients up to 10. Again, the number of oxysulfides is significantly lower .