The spin-restricted open-shell Hartree-Fock method (ROHF) can always be chosen to systems where all unpaired spins are parallel. The TURBOMOLE keywords for such a case (one open shell, triplet eg2 ) are:
$open shells type=1 eg 1 (1) $roothaan 1 a=1 b=2
It can also treat more complicated open-shell cases, as indicated in the tables below. In particular, it is possible to calculate the [xy] singlet case. As a guide for expert users, complete ROHF TURBOMOLE input for O2 for various CSFs (configuration state function) is given in Section 16.6. Further examples are collected below.
The ROHF ansatz for the energy expectation value has a term for interactions of closed-shells with closed-shells (indices k, l), a term for purely open-shell interactions (indices m, n) and a coupling term (k, m):
|E =||2hkk + (2Jkl - Kkl)|
|+ f[2hmm + f(2aJmn - bKmn) + 2(2Jkm - Kkm)]|