This book aims at providing graduate students and researchers with
funda- mental knowledge indispensable for entering the new field of
"microclus- 3 ters". Microclusters consisting of 10 to 10 atoms exhibit
neither the pro- perties of the corresponding bulk nor those of the
corresponding molecule of a few atoms. The microclusters may be
considered to form a new phase of materials lying between macroscopic
solids and microscopic particles such as atoms and molecules, showing
both macroscopic and microscopic features. However, research into such"a
riew phase has been left untouched until recent years by the development
of the quantum theory of matter. The microscopic features of
microclusters were first revealed by ob- serving anomalies of the mass
spectrum of a Na cluster beam at specific sizes, called magic numbers.
Then it was experimentally confirmed that the magic numbers come from
the shell structure of valence electrons. Being stimulated by these
epoch-making findings in metal microclusters and aided by progress of
the experimental techniques producing relatively dense, non- interacting
micro clusters of various sizes in the form of micro cluster beams, the
research field of microclusters has developed rapidly in these 5 to 7
years. The progress is also due to the improvement of computers and com-
putational techniques, which have made it possible to perform ab initio
cal- culations of the atomic and electronic structure of smaller
microclusters, as well as to carry out computer simulations of their
dynamics.