We have investigated electronic structures of La$_3$S$_4$ and Ce$_3$S$_4$ using the LSDA and LSDA+$U$ methods. Calculated density of states (DOS) are compared with the experimental DOS obtained by the valence band photoemission spectroscopy. The DOS at $E_{rm{F}}$ indicates the 5$d$ character in La$_3$S$_4$ and 4$f$ character in Ce$_3$S$_4$. It is found to be nearly half metallic in the ferromagnetic ground state of Ce$_3$S$_4$. %Ce$_3$S$_4$ has ferromagnetic ground states with spin and orbital magnetic %moments of 1.27 $mu_{rm{B}}$ and $-$2.81 $mu_{rm{B}}$ per Ce, respectively, %and shows nearly half metallic ground state. We discuss the superconductivity and structural transition in La$_3$S$_4$, and the absence of structural transition in Ce$_3$S$_4$.
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