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_{g}^{2} ) 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 O_{2} for various CSFs (configuration state function) is given in Section 18.6. 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 = | 2h_{kk} + (2J_{kl} - K_{kl}) | |
+ f[2h_{mm} + f(2aJ_{mn} - bK_{mn}) + 2(2J_{km} - K_{km})] |