Explain opposing defect-concentration trends across crystal structures

Establish the mechanistic origin of the opposing correlations between saturated defect concentrations and vacancy-migration-related properties in BCC metals versus FCC and HCP metals.

Background

The tabGAP simulations show that defect concentration increases with vacancy migration energy in BCC metals but decreases with vacancy migration energy in FCC and HCP metals. Similar opposing behavior appears when defect concentration is compared with experimental recovery-stage-III temperatures.

Although the distinction may relate to the different packing structures, the paper does not identify the mechanism responsible. The limited number of FCC and HCP tabGAP systems and the fact that some materials have not reached saturation add uncertainty, motivating further investigation.