First Principle Surface Analysis of YF₃ and Isostructural HoF₃

Area of Science:

• Materials Science
• Computational Chemistry
• Solid State Chemistry

Background:

• Yttrium and holmium trifluorides (YF3, HoF3) are studied due to their similar geochemical behavior, classifying them as a geochemical twin pair.
• Yttrium is often grouped with rare earth elements (REE) as REE+Y, highlighting their related properties.

Purpose of the Study:

• To investigate the surface stability of YF3 and HoF3 using periodic density functional theory (DFT).
• To compare the surface properties of these two geochemical twins and identify subtle differences.

Main Methods:

• Periodic density functional theory (DFT) calculations were employed.
• Bulk HoF3 was best described by DFT/DFT+U when 4f-electrons were excluded from the valence region.
• Surface stability was analyzed using 2D slab models for YF3 (PBE) and HoF3 (PBE+Ud/3 eV/4f-in-core).

Main Results:

• An extensive surface stability analysis considered all seven low-lying Miller indices surfaces with various stoichiometric and substoichiometric terminations.
• Wulff plots indicated dominance of the stoichiometric (010) surface for both YF3 and HoF3.
• Subtle but significant differences in surface stability were identified between YF3 and HoF3.

Conclusions:

• The study provides insights into the surface properties of YF3 and HoF3, crucial for understanding their behavior in various applications.
• Despite being geochemical twins, YF3 and HoF3 exhibit distinct surface characteristics.
• DFT methods, particularly with adjustments for 4f-electrons in HoF3, are effective for studying these materials.