3
$\begingroup$

I want to create the CIF file of CuI using VESTA software.I used the following parameters to create my CIF : space group, lattice parameter, the angles (alpha, beta and gamma), atomic positions of Cu and I.

In the experimental data of my material they mention : Rwp ,RI,Rf and atomic displacement parameter B, as shown in the picture bellow . I don't know the meaning of those parameters and if I should include them in my CIF file how to do that using VESTA?

enter image description here

Please, Clarify my doubts! It will be helpful to me in my learning process. Thank you

$\endgroup$
2
  • $\begingroup$ The CIF file is a text file with the information about your system. If you have all the required data, just use any text editor, add the info with the respected fields, and then save as .CIF. For information about the CIF format you can consult this link. $\endgroup$
    – Camps
    Feb 20, 2023 at 17:19
  • $\begingroup$ @Camps Thank you, but I know how to create a CIF file. However I have some doubts that i want someone to clarify for me. Can you please read what i posted in case you can help. $\endgroup$
    – Camilla
    Feb 20, 2023 at 22:24

1 Answer 1

2
$\begingroup$

Answer: no, you don't need to include those parameters (Rwp, RI, Rf) in your CIF file.

If you want to visualize the space where the atom can move due thermal effects, you should add the atomic displacement parameter B.

Those parameters (Rwp, RI, Rf) have to do with the Rietveld refinement method and MEM-based pattern fitting used to determine the crystal structure from a powder diffraction pattern and electronic density data:

Figure of merits:
Since refinement depends on finding the best fit between a calculated and experimental pattern, it is important to have a numerical figure of merit quantifying the quality of the fit. Below are the figures of merit generally used to characterize the quality of a refinement. They provide insight to how well the model fits the observed data.

From Rietveld refinement

Profile residual (reliability factor): $${\displaystyle R_{p}=\sum _{i}^{n}{\frac {|Y_{i}^{\text{obs}}-Y_{i}^{\text{calc}}|}{\sum _{i}^{n}Y_{i}^{\text{obs}}}}\times 100\%}$$

Weighted profile residual: Weighted profile residual: $${\displaystyle R_{wp}=\left(\sum _{i}^{n}{\frac {w_{i}(Y_{i}^{\text{obs}}-Y_{i}^{\text{calc}})^{2}}{\sum _{i}^{n}w_{i}(Y_{i}^{\text{obs}})^{2}}}\right)^{\frac {1}{2}}\times 100\%}$$

Bragg residual:
$${\displaystyle R_{B}=\sum _{j}^{m}{\frac {|I_{j}^{\text{obs}}-I_{j}^{\text{calc}}|}{\sum _{i}^{n}I_{j}^{\text{obs}}}}\times 100\%}$$

Expected profile residual:
$${\displaystyle R_{\text{exp}}=\left({\frac {n-p}{\sum _{i}^{n}w_{i}(Y_{i}^{\text{obs}})^{2}}}\right)^{\frac {1}{2}}\times 100\%}$$

Goodness of fit:
$${\displaystyle \mathrm {X} ^{2}=\sum _{i}^{n}{\frac {(Y_{i}^{\text{obs}}-Y_{i}^{\text{calc}})^{2}}{n-p}}=\left({\frac {R_{wp}}{R_{\text{exp}}}}\right)}$$

From Maximum Entropy Method (MEM) based pattern fitting (MPF)

Reliability factor:
$${\displaystyle R_{l}=\sum _{h}{\frac {|I^{\text{obs}}(h)-I^{\text{calc}}(h)|}{\sum _{h}I^{\text{obs}}(h)}}}$$

References:

  • H. M. Rietveld. A profile refinement method for nuclear and magnetic structures. Journal of Applied Crystallography, 2(2), 65–71 (1969). doi:10.1107/s0021889869006558.
  • M. Takata , E. Nishibori and M. Sakata. Charge density studies utilizing powder diffraction and MEM. Exploring of high Tc superconductors, C60 superconductors and manganites. Zeitschrift für Kristallographie - Crystalline Materials. 216, 71–86 (2001). doi:10.1524/zkri.216.2.71.20335
  • F. Izumi. Beyond the ability of Rietveld analysis: MEM-based pattern fitting.. Solid State Ionics 172, 1–6 (2004). doi:10.1016/j.ssi.2004.04.023
$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .