  Structural and optical properties of several high light output halide
scintillators and closely related materials are presented based on first
principles calculations. The optical properties are based on the Engel-Vosko
generalized gradient approximation and the recently developed density
functional of Tran and Blaha. The materials investigated are BaBr$_2$, BaIBr,
BaCl$_2$, BaF$_2$, BaI$_2$, BiI$_3$, CaI$_2$, Cs$_2LiYCl$_6$, CsBa$_2$Br$_5$,
CsBa$_2$I$_5$, K$_2$LaBr$_5$, K$_2$LaCl$_5$,K$_2$LaI$_5$, LaBr$_3$, LaCl$_3$,
SrBr$_2$, and YI$_3$. For comparison results are presented for the oxide
CdWO$_4$. We find that the Tran Blaha functional gives greatly improved band
gaps and optical properties in this class of materials. Furthermore, we find
that unlike CdWO$_4$, most of these halides are highly isotropic from an
optical point of view even though in many cases the crystal structures and
other properties are not. This general result is rationalized in terms of
halide chemistry. Implications for the development of ceramic halide
scintillators are discussed.
