Two-electron F' centers in alkali halides: a saddle point approach. I. General and semicontinuum analyses

TL;DR

This paper investigates the behavior of F' centers in alkali halides, focusing on their displacement and saddle point configurations using a semicontinuum approach to understand their electronic states.

Contribution

It introduces a saddle point analysis of two-electron F' centers, providing a theoretical framework for calculating their eigenenergies and stability in different configurations.

Findings

F' centers can displace along <110> due to vibrational coupling.

The saddle point configuration resembles a diatomic molecule.

Calculations determine the more energetically favorable configuration.

Abstract

The F' center in an alkali halide forms when an anion vacancy traps two electrons which is the prerequisite of a diatomic molecule. Indeed, the center may displace left or right along <110> in a (110) plane, due to its coupling to the B_{1u} vibrational mode of <110> polarization respectively. On jumping from the initial position to the final position the F' center passes through a saddle point which configuration is molecule-like being conformed by two neighboring semi-vacancies along <110>. Each semi-vacancy traps one electron to change its effective charge from +1/2 to -1/2 formin a semi-F' center. We ouline the basic theory so as to perform calculations on the F' eigenenergies in the two configurations to see which one of them is more favorable.