  To understand the magnetism of VSe$_2$, whose monolayer form has recently
been reported to be a room temperature ferromagnet, Here, the combined method
of conventional density functional theory with dynamical mean-field theory has
been adopted. This higher-level computation method enables us to resolve many
of existing controversies and contradictions in between theory and experiment.
First of all, this new approach is shown to give the correct magnetic
properties of both bulk and two-dimensional limit of VSe$_2$ which demonstrates
its superiority to the conventional methods. The results demonstrate that
monolayer VSe$_2$ without charge density waves is a ferromagnet with ordering
temperature of 250K. From the direct simulation of temperature-dependent
magnetic susceptibility and ordered moment, it is shown that its ferromagnetism
is clearly two-dimensional in nature. Further, it is shown that this
ferromagnetic order is vulnerable to extra charge dopings which provides the
important insight to elucidate recent experimental controversies.
