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I'm currently doing some research on perovskite structures and I'm curious about finding out the properties of the orthorhombic lattice. So the cubic structure was easy enough since all sides are the same, just calculate for the Goldschmidt Tolerance Factor and plug that value into equations to solve for a predicted stable lattice constant, to which I can set a range in which I can make energy calculations to determine the stable lattice constant. I'm just curious about how to approach modeling the orthorhombic structure in general. That is, how do I go about finding a, b, and c? Been looking around but as of yet I haven't found the answer I'm looking for.

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    $\begingroup$ Maybe I've misunderstood the question, but don't you just do a geometry optimisation with variable cell? I think QE calls it "vc-relax". $\endgroup$ Commented Mar 16, 2022 at 0:23
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    $\begingroup$ @PhilHasnip - Coincidentally, after looking around a bit more with the right keywords I found out what I was looking for. I was looking for a set of empirical formulas that could do this, and I found a paper about prediction of lattice constants for orthorhombic perovskites. So I intend to use that as a reference for comparison for when I do vc-relax on QE. Thank you so much for answering. $\endgroup$
    – tumblewush
    Commented Mar 16, 2022 at 0:55
  • $\begingroup$ I'm glad you found your answer! Perhaps you could write an answer here, for the benefit of future readers? $\endgroup$ Commented Mar 16, 2022 at 1:05

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Posted this question mainly because I was trying to find empirical formulas that could help predict the values of a, b, and c for the orthorhombic perovskite structure, just as there are formulas for the prediction of lattice constants for cubic structures. And then I'd use these predicted values as a comparison for when I perform vc-relax optimizations on the crystal that I'm working with to see if the results are close.

After posting this question, looked around and I found THIS paper by R. Ubic and G. Subodh where they managed to derive an empirical correlation between ionic radii and lattice constants and, thus, a set of formulas that could be used for the prediction of values of a, b, and c for orthorhombic perovskites. Thanks to Phil Hasnip for answering my query.

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  • $\begingroup$ it's always okay to accept your own answer as well, it helps the site's statistics a little bit and tells those doing searches in the future that the question has an accepted answer. $\endgroup$
    – uhoh
    Commented May 17, 2022 at 17:38

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