The initial guess for the wave function, either the H core or the Hückel guess, had
little impact on the smoothness (or lack thereof) on the PECs for ScO. The Hückel
guess for YO was able to determine a single state as the bond length was increased,
whereas the H core guess produced oscillations between two distinct states near
dissociation.
The ground state for ZrO is
3 A 1 (see Fig. 6) along with a degenerate
3 A 2 state,
yet at 2.6 Å, the lowest energy state is found to be
3 B 2 when the H core initial guess
is used. When using the Hückel guess, at 2.4 Å, the PEC jumps to a
3 B 1 state,
which is the direct product of A 1 and B 1 singly occupied orbitals. Then at 2.6 Å the
calculation settles to a
3 A 1 state. However, this A 1 state results from the direct
product of two B 1 orbitals instead of two A 1 orbitals, as with the ground state
around the minimum of the curve. This is a direct result of different d-orbital
Fig. 4 Points calculated for ScO at the ROHF level of theory, using both the H core and Hückel
initial guesses
Fig. 5 Points calculated for YO at the ROHF level of theory, using both the H core and Hückel
initial guesses
The Importance of Orbital Analysis
15