  This article discusses the pressure-induced structural phase transition and
related phonon, electronic and optical properties of hexagonal {\epsilon}-GaSe
using first-principles calculations. The study focuses on optimizing geometric
and electronic band structures, analyzing the charge density distributions,
atomic vibrations, and phonon spectra, and characterizing the optical
properties of GaSe under hydrostatic pressure. The work also includes an
analysis of the phase transformation mechanism using the solid-state Nudged
Elastic Band (SS-NEB) method. This research sheds light on the physics of
structural phase transitions in layered materials and offers potential for the
development of pressure-manipulated electronics or optoelectronics.
