Nacl wyckoff positions

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Sample Input for FROZSL: NaCl

Richard Demille Wyckoff — was an early 20th-century pioneer in the technical approach to studying the stock market. At age 15, he took a job as a stock runner for a New York brokerage. Afterwards, while still in his 20s, he became the head of his own firm. He also founded and, for nearly two decades wrote, and edited The Magazine of Wall Streetwhich, at one point, had more thansubscribers. Wyckoff was an avid student of the markets, as well as an active tape reader and trader. He observed the market activities and campaigns of the legendary stock operators of his time, including JP Morgan and Jesse Livermore. From his observations and interviews with those big-time traders, Wyckoff codified the best practices of Livermore and others into laws, principles and techniques of trading methodology, money management and mental discipline. From his position, Mr. Wyckoff observed numerous retail investors being repeatedly fleeced. The school's central offering was a course that integrated the concepts that Wyckoff had learned about how to identify large operators' accumulation and distribution of stock with how to take positions in harmony with these big players. His time-tested insights are as valid today as they were when first articulated. This article provides an overview of Wyckoff's theoretical and practical approaches to the markets, including guidelines for identifying trade candidates and entering long and short positions, analysis of accumulation and distribution trading ranges and an explanation of how to use Point and Figure charts to identify price targets. Although this article focuses exclusively on stocks, Wyckoff's methods can be applied to any freely-traded market in which large institutional traders operate, including commodities, bonds and currencies. The Wyckoff Method involves a five-step approach to stock selection and trade entry, which can be summarized as follows:. Determine the present position and probable future trend of the market. Is the market consolidating or trending? Does your analysis of market structure, supply and demand indicate the direction that is likely in the near future? This assessment should help you decide whether to be in the market at all and, if so, whether to take long or short positions. Use both bar charts and Point and Figure charts of the major market indices for Step 1. Select stocks in harmony with the trend. In an uptrend, select stocks that are stronger than the market. For instance, look for stocks that demonstrate greater percentage increases than the market during rallies and smaller decreases during reactions. In a downtrend, do the reverse — choose stocks that are weaker than the market. If you are not sure about a specific issue, drop it and move on to the next one. Use bar charts of individual stocks to compare with those of the most relevant market index for Step 2. Therefore, if you are planning to take long positions, choose stocks that are under accumulation or re-accumulation and have built a sufficient cause to satisfy your objective. Step 3 relies on the use of Point and Figure charts of individual stocks. Determine the stocks' readiness to move. Apply the nine tests for buying or for selling described below.

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By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry. It only takes a minute to sign up. I'm somewhat confused by the concept of Wyckoff positions in crystal structures. From Quantum Chemistry of Solids by Robert Evarestov, the definition of a Wyckoff position is "all the crystallographic orbits which have the same not only isomorphic, but the same site-symmetry group". I was okay with this, but he then went on to define equivalent Wyckoff positions as positions such that "equivalent sites have the same point-group symmetry and the same orientations of symmetry elements with respect to the lattice". What I fail to understand is how the equivalent Wyckoff positions don't collapse to a single Wyckoff position, as they seem to meet the criteria of having the same site-symmetry. Is there a clear explanation of what distinguishes two Wyckoff positions enough to be equivalent, but not just a single position? As is seen from the table, the pairs of points a-b and f-g not only have isomorphic, but also equivalent Wyckoff positions. The equivalent sites have the same point group symmetry and the same orientations of symmetry elements with respect to the lattice. It seems to me that care has to be taken with the words 'equivalent' and 'same' in the definitions above. Equivalent positions do not mean the same position. In the case, say, of a 4 fold axis any point say in the first quadrant can be replicated to the other three quadrants and these are equivalent points but not the same point, clearly. In some cases such as with reflections in a plane, two sets of identical or equivalent points may be produced and so and the number of equivalent points is reduced. The number of equivalent sets is called the multiplicity. These have been called special positions when they lie on a symmetry element. A position 2f, for example, indicates two equivalent atoms at position given by symmetry f. For each space group a table of general and special positions can be made. This includes point symmetries, positions multiplicities and Wycoff symbols. The table below shows examples. Table copied from page 75 of 'Introduction to Crystallography' by D. Sands, publ. I believe I have identified what my misunderstanding was. I was incorrectly conflating point group symmetry with site symmetry, which is a subgroup of the overall point group symmetry that leaves the given position unchanged. So, it is possible for two points to have equivalent site symmetries while not having the same site symmetry, e. The orbits from these generating points would not be conjugate and so they would be put into separate Wyckoff positions. However, depending on where you choose the origin to be, the different Wyckoff positions can interchange the generating points of their orbits, making them equivalent positions. An explicit example of this is Rock salt NaCl space group Nwhere either Na or Cl can placed at Wyckoff position a while the other is placed at b. Formally, equivalent Wyckoff positions are those which can be transformed into each other by applying the generators of the Euclidean normalizer. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Understanding Equivalent Wyckoff positions Ask Question. Asked 1 year, 8 months ago. Active 1 year, 8 months ago. Viewed 3k times. Tyberius Tyberius 9, 3 3 gold badges 26 26 silver badges 72 72 bronze badges. Active Oldest Votes. Sign up or log in Sign up using Google.

Crystal Structure Databases


NaCl has a cubic unit cell. It is best thought of as a face-centered cubic array of anions with an interpenetrating fcc cation lattice or vice-versa. The cell looks the same whether you start with anions or cations on the corners. Each ion is 6-coordinate and has a local octahedral geometry. Notice that the plane is hexagonally closest packed. Something that surprises novices is that the plane does not contain the body centered atom. Take a look at the models above and below to convinvce yourself of this very important fact! Here is a polyhedral representation of the NaCl unit cell. We could have drawn octahedra around either of the two atoms. In the case below, we have drawn them around the corner atoms and changed the color to improve the image contrast:. Shown here is a Chime model you can rotate and manipulate. I need to update these to jmol; just haven't found the time yet Notice that you can see alternating hcp layers that contain only Na and only Cl atoms if you manipulate it correctly. See the drawing of the plane shown above if this orientation is not clear.

Structure World


Wyckoff Positions Splitting Splitting of the Wyckoff positions As an input data the program needs the numbers of both groups as given in the International Tables for Crystallographyvol. A, and the transformation matrix that relates the basis of the supergroup with that of the subgroup. If you do not know the numbers of the groups, use the buttons [choose it] to select them from the table with the space groups symbols. If you do not know the transformation relating both bases, use the link to the other programs on the Bilbao Crystallographic Server to find it. When all of the input data is complete, click on the button [Show group-subgroup data] to see the list with the Wyckoff positions of the group and select the one for which the splitting should be calculated. Splitting of the Wyckoff positions If you are interested in other publications related to Bilbao Crystallographic Server, click here. Conventional Settings. Please, enter the sequential numbers of group and subgroup as given in International Tables for Crystallography, Vol. Enter supergroup or. Enter subgroup or. Please, define the transformation relating the group and the subgroup bases. NOTE: If you don't know the transformation click here for possible workarounds. For comments, please mail to administrador.

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Chemistry - Liquids and Solids (36 of 59) Crystal Structure: Ionic NaCl



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