# Sign of exchange integral in quantum chemistry?

I have a question about exchange integral in quantum chemistry.

Usually, we learn that the sign of exchange integral is positive, so a triplet state has lower energy than singlet state.

Is it possible that the exchange integral has a negative sign? If possible, in what case the exchange integral becomes negative?

Thank you!

$$\textbf{Note :}$$ This is a preliminary vague answer to OP's question. Will soon be expanded with reasonable rigour and details.