In Depth First-Principles Investigation of Phase Stability, Structural, Vibrational, Electronic, Elastic, and Piezoelectric Properties in Vanadium-Based Janus Dichalcogenide Monolayer VBrSe

First-principles calculations based on density functional theory (DFT) were employed to investigate systematically the structural, electronic, vibrational, elastic, and piezoelectric properties of monolayer Janus VBrSe in both 2 H and 1 T phases. Phonon dispersion analysis indicates dynamic instability of the 1 T phase at ambient conditions, as evidenced by the presence of imaginary frequencies, thereby excluding it from further consideration. Conversely, the 2 H phase is confirmed to be dynamically stable and energetically favorable, supporting its feasibility for experimental synthesis. The 2 H -VBrSe exhibits a direct band gap, with its electronic structure demonstrating pronounced sensitivity to surface-induced strain effects, distinguishing it from conventional transition metal dichalcogenides (TMDs). Calculated Raman spectra provide characteristic vibrational modes enabling experimental phase identification. Notably, the 2 H phase exhibits substantial out-of-plane piezoelectric coefficients, highlighting its potential for applications in energy harvesting and piezoelectric devices. These findings position 2 H -VBrSe as a promising candidate for sensors, optoelectronic components, flexible electronics, and spintronic applications owing to its tunable band gap and strong piezoelectric response. This study offers critical insights into the phase stability and multifunctional properties of Janus VBrSe, laying the groundwork for its experimental realization and integration into next-generation technologies.