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# Evaluation of One-Electron Properties

Code author: Robert M. Parrish and Andrew C. Simmonett

Section author: Andrew C. Simmonett

PSI4 is capable of computing a number of one-electron properties summarized in the table below. The properties will be computed from the last computed one-particle density, using the following syntax:

    oeprop("MO_EXTENTS", "MULTIPOLE(4)", title = "hello!")

The named argument, title, is completely optional and is prepended to any globals variables set during the computation. The unnamed arguments are the properties to be computed. These can appear in any order, and multiple properties may be requested, as in the example above. Note that, due to Python syntax restrictions, the title argument must appear after the list of properties to compute. The available properties are shown in the table below.

Current one-electron property capabilities of PSI4
Feature | Keyword | Notes
--- | --- | ---
Electric dipole moment | DIPOLE |
Electric quadrupole moment | QUADRUPOLE | Raw (traced) moments and traceless multipoles
All moments up order N | MULTIPOLE(N) | Only raw (traced) moments. Sets global variables e.g. “DIPOLE X”, “32-POLE XYYZZ”
Transition dipole moment | TRANSITION_DIPOLE |
Transition quadrupole moment | TRANSITION_QUADRUPOLE |
Electrostatic potential, at nuclei | ESP_AT_NUCLEI | Sets global variables “ESP AT CENTER n”, n = 1 to natoms
Molecular orbital extents | MO_EXTENTS |
Mulliken atomic charges | MULLIKEN_CHARGES |
Löwdin atomic charges | LOWDIN_CHARGES |
Wiberg bond indices | WIBERG_LOWDIN_INDICES | Uses (Löwdin) symmetrically orthogonalized orbitals
Mayer bond indices | MAYER_INDICES |
Natural orbital occupations | NO_OCCUPATIONS |

## Basic Keywords

Multipole moments may be computed at any origin, which is controlled by the global PROPERTIES_ORIGIN keyword. The keyword takes an array with the following possible values:

Allowed origin specifications
Keyword | Interpretation
--- | ---
[x, y, z] | Origin is at the coordinates, in the same units as the geometry specification
[“COM”] | Origin is at the center of mass
[“NUCLEAR_CHARGE”] | Origin is at the center of nuclear charge

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