**1. Introduction**

Much has been written and learnt about powder diffraction in last two decades. The journey that began in 1910 with the Bragg father-son duo publishing their first paper on crystal structure determination using ionization spectrometer, a century later there are still perks and connives that have not been widely explored [1–3]. The meticulous solution to the single crystal NaCl structure by the Braggs was achieved by solving symmetry equations for thousands of positions within a unit cell of unknown symmetry, without the help of modern computational prowess [3–8]. As Mike Glazer put it in very powerful words, "It was the gifted mind of Lawrence Bragg seeing symmetries in space and numbers that enabled them to reach a solution much quickly than anticipated" [3, 5]. In addition, W L Bragg's consideration of diffraction from crystals as merely reflections from crystal planes, simplified the theory around the structure determination considerably [9]. In just

few months, Braggs determined structure of NaCl, KCl, KBr, CaF2, Cu2O, ZnS, NaNO3, some calcites and diamond from their respective single crystals [10].

The year 1914, Max von Laue was awarded Noble prize for his discovery of the diffraction of X-rays by crystals [11, 12] followed by 1915 prize for their services in the analysis of crystal structure by means of X-rays to W H and W L Bragg [6] itself concatenates the importance of crystal structure determination. In following years, Debye and Scherrer extended the theory from single crystal to powder diffraction, presenting the complete theory of powder diffraction patterns and crystal structures used today (*squared sums of hkl ordered triplets*) [13–16]. Although Scherrer, Debye and Hull solved structures of many materials, it was not until modern computational boom that new, more complex and low symmetry system could be solved via powder diffraction pattern [17–23]. In the quest of achieving a suitable pathway for attaining a solution of powder X-ray diffraction many niche-limited attempts like maximum likelihood method [24, 25], anomalous dispersion, maximum entropy method, line profile fitting [26] etc. were made abundantly in 1950s and 60s. Hugo Rietveld in 1960s came up with one such method, employing least square iteration principle to statistically estimate the weighted contribution of every point on a powder XRD pattern [27]. The method now known as Rietveld refinement was the first step towards full profile whole powder pattern fitting method for x-ray and neutron diffraction data.
