Conventional magnetism occurs in systems which contain transition metal or rare earth ions with partially filled d or f shells . In practice , all systems which have been studied or used in devices in the past , contain transition metals or rare earth ions . Recent experimental and/or theoretical observations of magnetism in systems with no valance d or f electron challenge our In this project , we employ density functional theory and ultrasoft pseudopotential calculation to study magnetism in binary compounds CaN and CaAs . Regarding the structure of analogous magnetic materials and experimental results of CaAs synthesis , we have considered two cubic structures : rocksalt (RS) and zinc-blende (ZB) , and four hexagonal structures : NiAs , wurtzite (WZ) , anti-NiAs , and NaO . The calculated results show that CaN in cubic , NiAs , and wurtzite structures , and CaAs only in zinc-blende phase have ferromagnetic ground states with a magnetic moment of 1 µ B . Electronic structure analysis of these materials indicates that magnetism originates from anion p states . Existence of flat p bands and consequently high density of states at the Fermi level of magnetic structures give rises to Stoner spin splitting and spontaneous ferromagnetism . Larger exchange interaction in 2p orbital of nitrogen respect to 4p orbtial of arsenic causes that CaN has more structures with ferromagnetic ground state than CaAs . Slight hybridization with calcium d states increase density of states at the Fermi level and enhance ferromagnetism in system . The stability of all systems is studied from both thermodynamical and lattice dynamical point of view . We discuss that although all structures have negative heat of formation , except NaO phase , other structures possess imaginary phonon frequencies indicating dynamical instabilities . To find out the reason of instability , topology of electron charge density is investigated in all structures . According to the obtained result , the tendency of anion atoms to get close together and make covalent bonds is the origin of the observed dynamical instability . Anions in NaO phase have the shortest distance from each other among the all phases and special topology of charge density of this phase provide the strongest covalent bonds between anions in respect to the other phases. Keywords: CaN , CaAs , Ferromagnetism , Half-metal , p orbital magnetism , Stoner criterion , Lattice dynamics , Phonon frequency , Topology of electron charge density.
