  The discovery of ideal spin-1/2 kagome antiferromagnets Herbertsmithite and
Zn-doped Barlowite represents a breakthrough in the quest for quantum spin
liquids (QSLs), and nuclear magnetic resonance (NMR) spectroscopy plays a
prominent role in revealing the quantum paramagnetism in these compounds.
However, interpretation of NMR data that is often masked by defects can be
controversial. Here, we show that the most significant interaction strength for
NMR, i.e. the hyperfine coupling (HFC) strength, can be reasonably reproduced
by first-principles calculations for these proposed QSLs. Applying this method
to a supercell containing Cu-Zn defects enables us to map out the variation and
distribution of HFC at different nuclear sites. This predictive power is
expected to bridge the missing link in the analysis of the low-temperature NMR
data.
