  We present a method to build magnetic models for insulators based on
high-temperature expansions by fitting both the magnetic susceptibility and the
low temperature specific heat data. It is applied to the frustrated magnet
kapellasite (Cu3Zn(OH)6Cl2) with the J1-J2-Jd-Heisenberg model on the kagome
lattice. Experimental data are reproduced with a set of "competing" exchange
energies closed to J1 = -12K, J2= -4K and Jd=15.6K, where Jd is the third
neighbor exchange energy across the hexagon. Strong constrains between these
exchange energies are established. These values confirm the results of B.
F{\aa}k et al. (Phys. Rev. Lett., 109, 037208 (2012)) regarding the location of
kapellasite in the {\it cuboc2} phase of the Heisenberg model. The quality and
limits of this modeling are discussed.
