Diffraction methods critical points

The chemical bonding and the possible existence of non-nuclear maxima (NNM) in the EDDs of simple metals has recently been much debated [13,27-31]. The question of NNM in simple metals is a diverse topic, and the research on the topic has basically addressed three issues. First, what are the topological features of simple metals This question is interesting from a purely mathematical point of view because the number and types of critical points in the EDD have to satisfy the constraints of the crystal symmetry [32], In the case of the hexagonal-close-packed (hep) structure, a critical point network has not yet been theoretically established [28]. The second topic of interest is that if NNM exist in metals what do they mean, and are they important for the physical properties of the material The third and most heavily debated issue is about numerical methods used in the experimental determination of EDDs from Bragg X-ray diffraction data. It is in this respect that the presence of NNM in metals has been intimately tied to the reliability of MEM densities. 

Zarzycki G (1957) The critical point data of refractory metals, aluminum oxide and uranium dioxide using the Hoch- Arpshofen method. J Phys Radium 18 65A-69A. Study of molten salts by x- ray diffraction. II. Structure in the liquid state of the chlorides LiCl, NaCl, KCl, BaCl2, and of the fluoride Cap2. General considerations on the structure of molten halides (1958) J Phys Radium 19 13A-19A... 

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