Natural Ionization Orbitlals

Introduction

A compact orbital representation of ionization processes is described utilizing the difference of calculated one-particle density matrices. Natural orbital analysis involving this difference density matrix simplifies interpretation of electronic detachment processes and allows differentiation between one-electron transitions and shake-up/shake-off transitions, in which one-electron processes are accompanied by excitation of a second electron into the virtual orbital space.

J. Chem. Phys. 144, 204117, (2016)

Use of the NIO Program

>> python NIO.py GroundState.fchk DetachedState.fchk
output: NIO-GroundState.fchk