The 2H-phase of monolayer vanadium diselenide (VSe \(_2\) ) has recently emerged as a very intriguing material in spintronics due to its intrinsic ferromagnetism with semiconducting properties. In the present work, first-principles based calculations have been employed to systematically study the electronic, magnetic, and optical behaviour of 2D VSe \(_2\) for investigating the impact of different external excitations such as strain, electric field, and pressure on the material. Specifically, the magnetic moment, band gap, Curie temperature (T \(_c\) ), and absorption coefficient could be modulated, as the states near the Fermi level are mainly contributed by the in-plane atomic orbitals. The presence of different electronic phases in 2D VSe \(_2\) can be modulated from semiconductor to half-metal and even normal metal under the influence of external stimuli. Furthermore, the in-plane biaxial strain can effectively tune the T \(_c\) and attains a maximum value of 354K at \(\eta _b\) = 6%. The maximum observed absorption coefficient is found to be 5.05 \(\times\) 10 \(^5\) cm \(^{-1}\) (at 1.4 eV) under the applied pressure of 30 GPa, indicating that the VSe \(_2\) exhibits strong light absorption in the visible region. The unique combination of electronic phases, robust ferromagnetism, and optical activity makes the 2H-VSe \(_2\) a suitable candidate for flexible electronic, optoelectronic, and spintronic applications.
