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 e) 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] case. As a guide for expert users, complete ROHF TURBOMOLE input for O for various CSFs (configuration state function) is given in Section 15.6. 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 ), a term for purely open-shell interactions (indices ) and a coupling term ():