# Notes on Options¶

Note

The options referred to in the Theoretical Methods: SCF to FCI section below and indexed in Keywords by Module are placed in set blocks as described in Job Control Keywords, not as arguments to a Python function (like energy()).

Note

All PSI4 keyword names and values are insensitive to case, both those that are placed in set blocks and as Python function arguments. The few exceptions are documented for the database() function, where case structure must match the database file.

Note

Boolean options can be specified by yes, on, true, or 1 for affirmative and no, off, false, or 0 for negative, all insensitive to case.

Note

Certain convergence and tolerance keywords, of type double (real numbers), may be specified using either a real number or an integer; and integer X is then treated as the number of converged decimal digits required. For example, to request as energy converged to $$10^{-6} E_h$$, the user may set the e_convergence keyword to 0.000001, 1.0e-6, or 6.

# Notes on PSI Variables¶

Note

Starting in 1.6, there are three standard ways to access an excited state property. We give examples below, but the method name and property name may change.

• method ROOT 0 -> ROOT m property to get root m.

• method ROOT 0 -> ROOT m property - h TRANSITION to get root m and independently specify that the total transition symmetry is h, e.g., A2.

• method ROOT 0 (h) -> ROOT m (i) property to get the transition between two roots, specifying the symmetry of both states and the index of the target roots among states of their own symmetry.

For example, to target the second excited-state, which is also the lowest energy state of its irrep, the first two calls will take m = 2, while the last takes m = 0. Methods that use this interface are: TD-fctl. Note that numberings are associated with the calculation much more strongly than with the molecular system. Changing the number of roots sought, the symmetry subspace or the symmetry apportionment of roots under which the computation is run, or the excited state method are all likely to scramble root numberings.