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.
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.