Dielectric and electronic structure modulation in andalusite through nitrogen and boron substitution: a first-principles study

Abstract

The dielectric and electronic properties of Al₂SiO₅ were studied using density functional theory (DFT) with the GGA PBE and meta-GGA r²SCAN functionals. The orthorhombic andalusite structure was optimized with each functional. Compared with PBE, r²SCAN gave lattice parameters closer to the experimental values and a larger band gap, and was therefore used to examine the substituted structures. Boron and nitrogen were introduced by replacing Al and O, respectively, while P substitution at the Si site was included for comparison. The PDOS of pristine andalusite shows a valence band dominated by O-2p states, with contributions from Al and Si near the conduction-band edge. Both B1 and B2 remained insulating after substitution, with B-O hybridization appearing in the valence band region. In contrast, N and P substitution produced states near the Fermi level. The charge-density-difference maps also show that the distribution of charge depends on the substitution site. B1 shows a more localized redistribution around the B-O region, whereas B2, N, and P produce more anisotropic redistribution. For the insulating B-substituted systems, the dielectric response increased slightly relative to pristine andalusite, accompanied by changes in the refractive index and absorption spectra. These findings indicate that the electronic and dielectric properties of andalusite depend on both the substituting element and its local coordination environment.