Screening effect imperfect

Before discussing screening, let us examine the effect of lattice imperfections on the electronic diffraction. The simplest defect is a vacancy, a missing ion at the site To. Any such change in atomic arrangement requires us to reevaluate the structure factors, which requires application of Eq. (16-5), We rewrite the sum with a prime to indicate the omission of the term i = 0, and write A — 1 to indicate the decrease in the number of ions by one ... 

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