The dark energy dominated warm dark matter ( WDM ) model is a promising alternative cosmological scenario .
We explore large-scale structure formation in this paradigm .
We do this in two different ways : with the halo model approach and with the help of an ensemble of high resolution N -body simulations .
Combining these quasi-independent approaches , leads to a physical understanding of the important processes which shape the formation of structures .
We take a detailed look at the halo mass function , the concentrations and the linear halo bias of WDM .
In all cases we find interesting deviations with respect to CDM .
In particular , the concentration-mass relation displays a turnover for group scale dark matter haloes , for the case of WDM particles with masses of the order m _ { WDM } \sim 0.25 { keV } .
This may be interpreted as a hint for top-down structure formation on small scales .
We implement our results into the halo model and find much better agreement with simulations .
On small scales the WDM halo model now performs as well as its CDM counterpart .