One-electron wavefunction obtained as a solution of the Schrödinger equation for an atom.
Sources:
Green Book, 2nd ed., p. 19 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1086 (https://doi.org/10.1351/pac199466051077)