Monte-Carlo calculation of binary AgnPbm (n plus m <= 28) clusters

Structural and electronic properties df mixed silver-lead AgnPbm (n + m les s than or equal to 28) clusters are studied. At the first stage, geometric configurations of the global and local energy minima of silver clusters Ag- n (n less than or equal to 28) are calculated by the Monte-Carlo method wit h the use of the Sutton-Chen potential of interaction between atomic partic les. Then silver atoms in a cluster of each size n were replaced by lead wi th a random choice of the substitution place. The extended Huckel method wa s applied to calculate the energy difference between the highest occupied a nd lower unoccupied molecular orbitals for the entire set of structures. Th is allowed us to estimate positions of the bands in UV spectra of the syste ms. After averaging over all conceivable cluster configurations a trend in the spectrum changes caused by variations of the lead fraction in the syste m is traced - as silver clusters were diluted with lead the UV-spectrum ban d is shifted to shorter wavelengths, which is consistent both with the resu lts of quantum-chemical calculations of AgPb and with the data of experimen ts performed with colloid silver-lead particles.