First-Principles Investigation on Structural Distortion and Electronic Tuning in La-Doped MgB₂ Superconductors

Abstract

Rare-earth doping is a promising strategy for enhancing the superconducting performance of magnesium diboride (MgB₂) superconductor by modifying its lattice structure and electronic band characteristics. In this study, first-principles Density Functional Theory (DFT) calculations were carried out using the CASTEP module to evaluate the structural and electronic effects of lanthanum (La) substitution at the magnesium site of MgB₂. A 2×2×2 supercell was constructed, and doping concentrations of 25%, 50%, and 75% were simulated. Geometry optimization, bond length measurement, electronic band structure, and density of states (DOS) analyses were performed using the GGA-PBESOL functional with validated convergence parameters. Results indicate that La doping introduces significant lattice expansion and La–B bond elongation, causing structural distortion due to its large ionic radius.