Abstract: In this paper, small silver clusters on (110) surface of AgBr- cyrstal are considered as latent image. The Ag clusters mentioned above were studied by using semi-empirical SCF molecular orbital method CNDO/2. From the results of calculation, the conclusions can be drawn as follows.(1) The optimized geometries of Ag₃ and Ag₄ were found to be isosceles triangle and trapezoid with their planes perpendicular to the (110) plane of AgBr crystal.(2) Ag₃ and Ag₄ clusters are polar. The polarity seems to be responsible for the catalytic effect in the development and accumulation of Ag atoms. Hence it may be an important property of the latent image.(3) Energetically, Ag₃ is the most stable one among the Agn clusters (n = 1-4). At the same time, Ag₃ is also the cluster to become polar, therefore Ag₃ may be the minimum size of the latent image.(4) The growth of the Ag cluster probably first occurs by an ionic event, followed by the trap of electron.

Key words: silver bromide crystal, silver cluster, quantum chemistry, semi-empirical molecular orbital method, CNDO