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## Why Reciprocal Space?

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 ```Newsgroups: sci.techniques.xtallography From: sul2@Lehigh.EDU Subject: Why reciprocal? Date: 4 May 1998 13:51:05 -0400 Hello, I have a couple basic questions about Miller's index plane and the reciprocal lattice. What is the reason that the (hkl) plane is designated for intersections at 1/h, 1/k, and 1/l, respectively? Why does it not simply use (hkl) for intersections at h,k and l? Likewise, why does the reciprocal lattice stand for 1/d(hkl)? I have read a few books saying that the reciprocal lattice (r*) is defined as r* = (b x c) / [a.(b x c)] and |r*| = area / volume = 1/height = 1/d(hkl) where a,b,c stand for unit vectors of primitive cell. It should be some reason to define r* in that way. Thank you Kai ```

 ```From: rwgk@laplace.csb.yale.edu (Ralf W. Grosse-Kunstleve) Newsgroups: sci.techniques.xtallography Subject: Re: Why reciprocal? Date: 04 May 1998 21:17:35 -0400 The reason is simply that crystallographers wanted a "simple" and convenient way of discribing x-rays diffracted by a crystal. Try to learn more about the "Ewald construction" and you will see how useful the mathematical concept of the reciprocal lattice is in helping you to understand the result of a diffraction experiment. As a start try Giacovazzo: Fundamentals of Crystallography or one of the older books by Buerger. The reciprocal lattice is just like a road atlas. A model which tells you which way x-rays go. Nothing more. Only how it relates to reality is slightly more involved. ```

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