It is proved that in slab simulations of uniform semiconductor surfaces the electric field in the vacuum space should vanish. In standard approach this condition was achieved by introduction of the dipole correction [J. Neugebauer and M. Scheffler, Phys. Rev. B 46, 16067 (1992)]. An effective and stable method of exact solution of Poisson equation, based on Laplace correction, which attains the zero field condition in the vacuum, is described. The dipole correction to the slab energy is removed. Additionally, a method of the control of electric field within the slab is introduced, applicable in direct simulations of Fermi level influence on the properties of semiconductor surfaces.
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