| Silver halides include AgCl,AgBr and AgI. Bulk silver halides are typical superionic conductors. Their conductivity increases with the temperature. Silver halides were applied widely in the fields of preparing heat-resistant conductor material, photograph, electrochemistry and metallurgy. So the studies on this system were received considerable attention. At present, There were much more theoretical and experimental studies on silver halides crystalline , but little research about the silver halides clusters' structures and properties.The possible stable structures of silver halides clusters were studied by using the modified genetic algorithm combined with the empirical potential. The calculation shows that the stable structures of (AgCl)n,(AgBr)n clusters are generally closely packed, and the stable structures of (AgI)n clusters mainly are cage composed of four-ring and six-ring or eight-ring. The results reflect that the chemical bond in (AgCl)n,(AgBr)n cluster is ionic bond with covalent character, and the bond in (AgI)n clusters is covalent bond with ionic character. According to the secondary differences of energy, (AgCl)n, n=4,6,8,9,13;(AgBr)n n=4,6,10;(AgI)n n=6,8,11 are specially stable.The stable structures of (AgBr)n(n≤6) clusters were further optimized at the level of B3P86/3-21G*.The initial structures used were the possible stable structures of (AgX)n (X=Cl,Br,I) (n≤6) clusters obtained from the GA's result. The calculation shows that the most stable structures of (AgBr)n(n≤3) are single-ring ,and the stable structures of (AgBr)n (n=4-6) are generally closely packed. The result reflects that the chemical bond in the small (AgBr)n clusters is covalent bond with strong ionic character. The average binding energy of (AgBr)n clusters increased rapidly when n≤3,and increased slowly when n>3, (AgBr)3 is specially stable. The energy gap of (AgBr)n(n=1-6) is 3.794eV～5.747eV, The larger energy gap indicates that the small (AgBr)n clusters are insulator. The Adiabatic electron affinities of (AgBr)n (n=2-6) are 1.15eV～2.57eV. The dipole moments of the most stable structures of (AgBr)n are zero except for (AgBr)5 The charges transferred from Ag to Br are 0.13～0.34 .The spectral analysis shows that (AgBr)2 have three strong vibration models and (AgBr)3 have seven strong vibration models .For the single-ring structure of (AgBr)2 and (AgBr)3, the respecting strongest IR frequencies are at 209.1601cm-1 and263.3180cm-1.
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