Optimization of out-of-plane polarization calculations for two-dimensional ferroelectric metals

Abstract Due to the screening effect of conduction electrons, ferroelectricity and metallicity typically do not coexist. However, recent studies have discovered metallic ferroelectricity in two-dimensional (2D) transition metal dichalcogenides, which show potential applications in ferroelectric tunneling junctions and ferroelectric memory. During the numerical calculations of the out-of-plane polarization using the classical dipole moment method, we find that significant inaccuracies arise when the reference point is chosen beyond a certain range, due to the unreasonable cut of the periodic charge density. The resulting computational inaccuracies can be suppressed by shifting the center of the two-dimensional materials to the lattice center. Furthermore, we show that asymmetry can be introduced when the real-space grid is not symmetrically distributed around the lattice center. Since the calculated charge density is the result of the real-space grid sampling, it is advisable to ensure that the grid is symmetrically distributed around the lattice center to avoid inaccuracies. The enhancement in precision of out-of-plane polarization calculations is helpful for the prediction of new ferroelectric metals (FEMs).