Numerical calculation of the complex berry phase in non-Hermitian systems

We numerically investigate topological phases of periodic lattice systems in tight-binding description under the influence of dissipation. The effects of dissipation are effectively described by $mathcal{PT}$-symmetric potentials. In this framework we develop a general numerical gauge smoothing procedure to calculate complex Berry phases from the biorthogonal basis of the systems non-Hermitian Hamiltonian. Further, we apply this method to a one-dimensional $mathcal{PT}$-symmetric lattice system and verify our numerical results by an analytical calculation.