Hi, I tried to calculate the nuclear magnetice hyperfine coupling constant in the RESPONSE part. Here's the output of my calculation of nitrix oxide. Both *ESR and *HFC modules contains Fermi-contact and spin-dipole directives but the results are different. I don't really understand why. BTW, may I ask the meanings of the notations: `<<FC;H>>, <<SD;H>>, <<PSO;SO>>`? Do they indicate the response values? [NO.out](/uploads/ca685e223125a37aa859e7ad58e8d96d/NO.out) See Line 1707 and Line 2647. Comparing the results with [the empirical constants](10.1021/j100091a064), I found the average value is closer to the experimental value. I did calculations for various diatomic molecules and made comparison with experimental values. Most of them imply the average value is a better choice, especially when large number of inactive obtials were used. Did I used an inappropriate setup? Thanks, Qianwei