I am trying to compute a H2 dissociation curve using UBLYP/SVP level of theory.
When the distance is far enough (~ 10 angstrom), closed shell with restricted BLYP and triplet with unrestricted BLYP give reasonable energies.
However, open shell singlet gives the same energy as the restricted one or never converge if electrons are assigned manually into two different orbitals ( ex, a 1, b 2 in define).
I expect that open shell singlet should give the same energy as triplet, and I am wondering whether I made something wrong in setting up the open shell singlet calculation.
I would appreciate any comments.