Optimizing CH2 triplet using MP2 and DFT, I am getting wrongly ordered molecular orbitals. a1,a1, b1,a1,b2. But for CH2, the order should be a1, a1, b2, a1, b1. I used differnt basis sets also did the swapping of molecular orbitals, to get the correct order. After swapping the MOs, only the listing order changed. Please help me to fix this problem.