# Notes on Options¶

Note

The Python options referred to in the Psithon Functions: Invoking a Calculation section below are placed as arguments to a Python function (like energy()), not in set blocks or commands.

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 one exception is documented for the subset option in 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

The derivative level type for optimize() and frequency() functions can be specified by energy, none, or 0 for 0th derivative, gradient, first, or 1 for 1st derivative, and hessian, second, or 2 for 2nd derivative. For finite difference, as opposed to analytic, derivatives, the POINTS option can be increased to 5 for greater accuracy at increased cost.

Note

Function option for the Psithon function called by the current function; the default is usually energy(). See Sec. Function Intercalls for a fuller description. Note that the value of the keyword is a Python object and so is not wrapped in quotes like a string.

Note

The molecule to be acted upon by the current function; the default is the “active” molecule, which is the nearest preceeding molecule declared in a molecule mymol {...} block or in an activate(mymol) statement. Note that the value of this keyword (mymol in the example) is a Python object and so is not wrapped in quotes like a string. Technically, this is a Molecule object.