  Based on the two flavor NJL model with a proper time regularization, we used
stationary wave condition (SWC) for the first time to study the influence of
the finite volume effects on the chiral phase transition of quark matter at
finite temperature. It is found that when the cubic volume size L is large than
LSWC = 500 fm, the chiral quark condensate is indistinguishable from that max
at L = $\infinity$,Here it should be noted that 500 fm is far greater than the
size of QGP produced at laboratory and the lattice QCD simulation space size.
It is also much larger than the previous limit size LAPBC = 5 fm estimated by
the commonly used anti-periodic boundary condition (APBC). max We also found
that when the space size L is less than LSWC = 0.25 fm, the spontaneous
symmetry min breaking concept is no longer valid. In addition, we first
introduce the spatial susceptibility, and through the study of the spatial
susceptibility, it was revealed for the first time that the chiral phase
transition caused by the finite volume effects in the nonchiral limit is a
crossover.
