  We investigate the structural, electronic and magnetic properties of the
newly synthesized mineral barlowite Cu4(OH)6FBr which contains Cu2+ ions in a
perfect kagome arrangement. In contrast to the spin-liquid candidate
herbertsmithite ZnCu3(OH)6Cl2, kagome layers in barlowite are perfectly aligned
due to the different bonding environments adopted by F- and Br- compared to
Cl-. We perform density functional theory calculations to obtain the Heisenberg
Hamiltonian parameters of Cu4(OH)6FBr which has a Cu2+ site coupling the kagome
layers. The 3D network of exchange couplings together with a substantial
Dzyaloshinskii-Moriya coupling lead to canted antiferromagnetic ordering of
this compound at TN=15 K as observed by magnetic susceptibility measurements on
single crystals.
