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5. 4In this article, we will use this terminology; by intrinsic surface states, we mean surface states characteristic of the “ideal” rearranged surface. The density of these intrinsic surface states should correspond to the total density of surface atoms. The term “extrinsic surface state” will be used for surface states induced by surface defects or impurities. The density of these states will normally correspond to the density of surface defects, imperfections, and impurities.