  Barlowite $Cu_4(OH)_6FBr$ is a newly found mineral containing $Cu^{2+}$
kagome planes. Despite similarities in many aspects to Herbertsmithite
$Cu_3Zn(OH)_6Cl_2$, the well-known quantum spin liquid (QSL) candidate,
intrinsic Barlowite turns out not to be a QSL, possibly due to the presence of
$Cu^{2+}$ ions in between kagome planes that induce interkagome magnetic
interaction [PRL, 113, 227203 (2014)]. Using first-principles calculation, we
systematically study the feasibility of selective substitution of the
interkagome Cu ions with isovalent nonmagnetic ions. Unlike previous
speculation of using larger dopants, such as $Cd^{2+}$ and $Ca^{2+}$, we
identify the most ideal stoichiometric doping elements to be Mg and Zn in
forming $Cu_3Mg(OH)_6FBr$ and $Cu_3Zn(OH)_6FBr$ with the highest site
selectivity and smallest lattice distortion. The equilibirium anti-site
disorder in Mg/Zn- doped Barlowite is estimated to be one order of magnitude
lower than that in Herbertsmithite. The single-electron band structure and
orbital component analysis show that the proposed selective doping effectively
mitigates the difference between Barlowite and Herbertsmithite.
