charges and other nonperturbative features of strong interactions. In recent years, three-dimensional configurations akin to domain walls became popular as well [@Ilgenfritz:2007xu; @Moran:2008xq; @Moran:2007nc; @deForcrand:2008aw; @deForcrand:2006my; @Zhitn]. First of all, these are the $Z(3)$ domain walls related to the center symmetry of the pure Yang-Mills theory [@deForcrand:2008aw] and double-layer domain wall structures in topological charge density [@Zhitn]. Lattice QCD serves as a main source of motivation and verification tool for these studies in pair with the theoretically appealing scenario of static quark confinement in the spirit of the dual Meissner effect equipped with the Wilson and Polyakov loop criteria. The localized configurations are characterized by the vanishing ratio of the action to the 4-volume in the infinite volume limit. In this sense, instantons, monopoles, vortices and double-layer domain walls are localized configurations.

A complementary treatment of the above mentioned overall task is based on the investigation of the properties of quantum effective action of QCD. As in other quantum systems with infinitely many degrees of freedom, the global minima of the effective action define the phase structure of QCD. The identification of global minima in different regimes (high energy density, high baryon density, strong external electromagnetic fields) has highest priority 