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I am looking for a program that can compare different structures and determine if they are equal or not. After performing DFT calculations, the obtained structures may be identical but for reasons like an alternative unit cell, numerical errors, etc., they might seem different.

Do you know any program to compare structures? The idea is that after DFT I will have loads of structures to compare and my aim is to find the different polymorphs. I know there is one called Sketch-map but my tutor says it is better to find another one.

Thanks!

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    $\begingroup$ +1 I want to first make sure that I know precisely what you mean. By "structure", do you mean what some people call "geometry", which is described by all bond lengths/angles, or by XYZ coordinates? What does it mean for two of these structures to be the "same"? I guess you have XYZ coordinates for the structures, and you need to know whether or not the bond lengths and angles that those XYZ coordinates describe, are the same to within some level of precision? In what format are your "structures" presented? $\endgroup$ Commented Jan 23, 2023 at 19:46

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If you have the crystal structure of each one of your systems, instead to try to overlay them and visually inspect each pair (depending on the number of structures this can be tedious and very feasible to errors), I strongly recommend you to generate the x-ray powder diffraction pattern for each crystal structure.

Each polymorph will produce a different powder diffraction pattern. Then, you plot all at the same time in your preferred graphics tools (Excel, Gnuplot, Origin, etc.) and can determine the difference among them.

The powder diffraction will take into account the cell parameters, the atomic positions and the type of atom in each position.

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  • $\begingroup$ Are there any web servers available to calculate the x-ray powder diffraction pattern given a crystal structure in PDB format? $\endgroup$
    – Vasista
    Commented Jan 24, 2023 at 9:43
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    $\begingroup$ You can use VESTA software. It is free and available for Linux/Windows. $\endgroup$
    – Camps
    Commented Jan 24, 2023 at 13:25

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