Dear all, I have just finished reading this technical paper in Sci.Rep., which definitely contains some interesting ideas. I am however puzzled by a few points:
1. The differences in cell parameters on using different ranges may well derive from the use of a “wrong” model, where “asphericity” of the form factors (their vectorial dependence) is not considered, nor anharmonicity of the atomic displacements is introduced. Nothing is said about particle sizes and their distribution, which typically is not gaussian (just to mention a few effects). This is physics and goes well beyond instrumental effects. To partially avoid this bias, one shoud try a parallel unbiased refinement by the Pawley or the Le Bail method (Armel…where are you?) 2. If the new criterion still is superior than Rwp, it’s difficult to claim that it is Necessary. Perhaps useful in many cases, but unapplicable if more complex phases, where peak broadening and severe overlap exist. The idea that it is a Necessary one calls to the Financial Interest sentence, where it is explicitely said that a patent on this work is pending. Does this mean that if someone (in the industrial environment, I suppose) adopts this criterion in his/her certifications, he/she can refrain from paying royaltees to Physonit Inc, being the choice of using it Necessary (i.e. unavoidable?) 1. The simple concept of average lattice parameter, when down to the 5th decimal digit, is clearly a nonsense, as it derives from too much idealization and is a consequence of numerical analysis. Note that in page 3 the cell parameter of LaB6 is given as 4.15686(0) angs. Yes, you read it correctly: (0)! Like a perfectly known number such as sqrt(2) or 3.14159, no matter how bad we are in measuring them experimentally. 2. Also, a Le Bail refinement cannot eliminate basic assumptions, such as cubic symmetry, absence of diffuse scattering, radiation spectrum shape, etc. 3. Finally, our structural analyses indicate that relative changes by T, P, stress, doping, etc., drive the differential functionality of these solids. Modern perovskites are appealing not because a = 6.12 angs, but because vacancies and interhalide dopings relatively change the overlap integrals of the frontier orbitals. So long for tonight Norberto Inviato dal mio telefono Windows 10
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